Measuring time of part of a track.

Use the Trim function. It shows the time, distance & pace, even before saving it. However, even if you save it, the trimming is fully reversible, hence you can restore the original anytime even if you save the trimmed activity.

Yea, thats the trick way. But I just want to select section on altitude graph and see whats the time for this section or avg speed, or avg heart beat etc. Now I have to devide the time by my self. It shows starting time and end time. Let say 5:35 and 23:10. jus one formula to show section time on screen. Just request for programers to add this data to graph data.

I recommend suggesting it to Garmin at Share Ideas | Garmin 

If you don't mind using a third party site on desktop, https://www.runalyze.com is free, syncs with your Garmin account, and can do what you want. (The site kinda works on mobile, but it's really meant for a big screen and some things don't work without a mouse.)

Just change the following settings first:

- Configuration > General Settings > Activity View > Plots: combination => Pace / Heart rate / Altitude

(this combines pace, HR and altitude on the same graph)

- Configuration > General Settings > Activity View > Plots: y-axis-scale type => reversed linear

(this makes the pace graph work similar to Garmin Connect. I also like to set Pace plot: y-axis maximum to something slow like 10:00/km, to avoid the Connect website problem where your pace graph is flattened out to the point of uselessness if you ever stop or walk.)

(When you hover or select an area on the graph, it will also highlight the same area on the GPS track / map, which I haven't screencapped.)