Instant pace is very slow to update

That's why I prefer the Lap Pace instead. If you keep it constant, it should match your instant pace most of the time.

Ok, but what's the point of the instant pace then, if I have to use the lap pace to replace it ?
And then, if I used the lap pace, I would not be able to use the green-red pace gauge to know how fast I have to go...
I should not have to search for hacky ways to be able to know something so essential as the instant pace in a dedicated running watch...

Anyway the question here is more on understanding if the 955 really is faster at adjusting to the real instant pace compared to the 255, because if the 955 really does take only 5 second to find the real pace (and in this case it would be usable) while the 255 takes 10-15 seconds to do the same thing (which is almost unusable), then this means the 255 has a bug of some kind, which can be reported to Garmin and fixed in future updates.
If not, then maybe my watch is faulty or maybe the 955 guy was underestimating the time it took for his watch to adjust.
So if somebody has a 255 or a 955 and does do interval workouts, write here how much your watch takes to reach the real pace value since the start of an interval.

Yep, you're right. We shouldn't have to search for these ways, but the instant pace is unusable for an interval training since the moment that the pace is displayed in 5 seconds steps (5:20, 5:25, 5:30...).

However, either the Lap Pace or the Average Pace are displayed in 1 second steps (5:21, 5:22, etc.), which is better to have your pace under control as long as you keep it constant, of course.

Not to mention the green-red pace gauge, which according to my own experience is good for a run based on HR, but not for a run based on pace due to this same thing of the 5 seconds steps. 

Anyway, I think that this 955 user was probably underestimating the time it took for his watch to adjust, or maybe you run in a place under hard GPS conditions.

I might be wrong but I think that 10-15 seconds is unfortunately acceptable with the current technology.

GNSS (using all+multiband) conditions were great: no buildings near me, no trees above me, and indeed the track on garmin connect was perfect, so that is definitely not the problem.

Anyway I have found some threads in this forum which seem to suggest that the pace gauge used for pace based workouts does not show the instant pace, but the step pace (or lap pace).
I really never tried to see what value the instant pace field in a personalized data screen was showing because I thought the pace gauge was showing the same thing.
If what they are saying is true, then the instant pace field should be more quick to update, it being really an instant value and not the mean of a value, which takes more time to rise or fall by definition.

Next time I will try to use the instant pace field and see how well that behaves compared to the pace gauge and if they were right.

i'm on training plan, and the control pace give me head-ache. satellite signal is good

you slow, you too fast arghhhh

I tried again and, to my surprise, the previous threads were wrong about the pace gauge (or probably Garmin changed the pace gauge with this new watch models): it has the same values as the "pace" data field, so that is the instant pace.
Indeed the lap pace, the step pace and the average pace values are different from the pace gauge.
I think this is good.

But the issue is still present: this instant pace value is very slow to update for interval training workouts.
It could be true that this is a limitation of gps based pace, however I've noticed that sometimes the watch is not so slow to update the pace value and only takes 3-5 seconds, while other times the change happens 15-20 seconds after the real change in pace. It seems to me that there is some kind of algorithm that chooses how often to update the value (and that the faster I run, the slowest it is to update, while a change in speed when I'm running slow gets detected faster). If this is the case, this algorithm should be improved to become usable during interval training or other similar workout types.

Does anybody else notice that the instant pace value changes more quickly sometimes and more slowly other times?

Unfortunatly, I have exactly the same problem. When I use the garmin training program for an intervall training, the instant pace is always wrong. 

For example,I had to run at 4:10 mn/km for 800 m, during all the training I stayed in the green zone of the pace gauge and at the end the lap pace was 4:30 min/km. 

So I had to run faster for all the training and, of course and the Garmin watch always says " too fast" 

for me, it's a real problem when you buy a specific watch for running to have your instant pace during your personnal training. 

Lately the watch has been way faster in catching the pace (instant pace field). I think it is doing so thanks to the accelerometer, used in conjunction to the gps.

I don't know if it is a firmware update that fixed it (right now I am on fw 12.27), but now it is responsive enough to be usable, and it is fast enough in noticing the change in pace when i do intervals, even if it is not super precise, but this can be overcome by getting a feeling for how this works.

(I'm always using all+multiband as I was before)

I have the same issue during interval, perfect conditions but fast running for 10 or 15 seconds will not show my current speed. which is difficult to track. please advise

The issue still remains, intervals are unusable in this condition. 

To me it looks like the pace will be rounded to 30 seconds, probably it was made in such a way that the voice assistant doesn't get confused by constantly changing pace. Who knows.. In any case, we don't have a momentary pace, but rounded ones. I always get the warning at the beginning that I'm too slow and at the end that I'm too fast. Lap pace is always correct, but instructions from the watch are misleading. And that's too complicated for Garmin to even understand the problem.