Customize/remove seconds on any built-in FR255 watchface?

Thank you for your question, I have been interested in it for a long time. Unfortunately I can't help you, I have FR245, it turned out that it does not have this option for all, but for some built-in digital Watch faces there is.  By the way, the always-on function for 255 is not relevant, so it cannot be disabled, its display is MIP and not OLED. Details of why this is so can be found directly in the thread on 255.

Always on seconds on MIP means that it runs a "partial update" every second instead of sleeping and just updating the screen once per minute. So it still uses more power. But it's less than the high power mode where it redraws the whole screen every second.

6125703 said:

But it's less than the high power mode where it redraws the whole screen every second.

Where did you get this information?

MIP(Memory In Picture) always redraws only the changed part of the screen, and only when something has changed, and not the entire screen. It remembers the picture and does not need to redraw it at any rate, and besides, it works on reflection and does not shine itself.

That is, it is always on and does not consume additional energy for this.

I think you may be confusing the MIP LCD display technology with the Garmin SDK. Yes, the MIP LCD hardware contains its own embedded "framebuffer" and keeps the pixels stable between writes.  But, as far as I can tell, the CIQ watchface app does not address and write to individual  MIP LCD pixels to change them.

According to the SDK docs, the CIQ framework calls for a full screen update once per minute in low power state and once per second in high power state. The SDK docs I have seen say that the framebuffer will be cleared for each full update call, and the app has to redraw all the pixels.

Optionally, there is a separate partial update call every second during the low power state. As far as I understand it, the app would set a smaller clipping box for this, e.g. just for the area with the seconds digits, and write all the pixels in that box during the partial update call.

I don't think the CIQ developer has access to the raw SPI interface to the display. They can only draw into an image buffer that the Garmin firmware will then copy into the LCD panel to perform the update.

Of course, we can't know exactly how the native Garmin apps work, but I wouldn't be surprised if they follow the same principles and essentially mapped the CIQ SDK interfaces onto the same rendering features they would use natively.

Look---the Garmin FR255 manual suggests using watchfaces that "don't update every second" to conserve battery. And the manual talks about using the Customize / Seconds menu to customize the seconds behavior for digital watchfaces. But then it doesn't actually provide this control for any of the built-in faces (at least not that I can find).

That's frustrating. I'm asking if anybody ever found a combination of settings for this. I thought I was pretty clear about this in the opening post.  I'm pretty sure that I have read Garmin literature referring to this constantly updating seconds display as "always-on seconds", but I don't really care. It's not a hill to die on...

The way I see it, it makes no sense to have seconds on the watchface, and not update them. If you want to save power, you can select a layout where there are no seconds shown.

I don't disagree, though I would settle for seconds that disappear in low power mode.

I checked various layouts for the default watchface I am using, and some of the optional layouts had only hours and minutes - no seconds.

On an FR255? If you don't mind, would you tell me how many distinct digital layouts you have?  I'm starting to wonder if I've lost some options due to "tidying up" actions I might have done when the watch was new. I don't remember it, but it's the kind of thing I tend to do, removing default menu items to simplify the UI for myself. (Though I would have assumed I could add such things back with the "+" option.)

When I use the "+" button to add, I only get a choice between digital and analog. And for the digital face, I only have 7 layout options. Of those, I only see 2 that don't have seconds. But, I guess I've been ignoring them as they also only have a couple data fields and I'm not interested in a watchface with no data...

I have the FR255 non-music, if that matters.

Sounds like the same I have. I have the Music version. 
I don't want too much data on the watch face. I go to the glances to see data when I need it. And I mostly want the data during activities anyway, but then I never use the watchface.