Do you mean a stopwatch or timer outside of an activity? Or within a timer for intervals?
I can’t say what a FR35 is capable of but I have a FR945 and it is able to do all of that.
For the later you would have to create a workout with intervals and then set a data field to ‘time left’ (not sure what it is actually called). For the stopwatch you can have data fields for either total workout time or lap time. So if you hit the lap button it would reset that field to zero and count up until you hit the lap button again.
For outside of an activity I can press and hold the backlight button to bring up the ‘controls’ menu and within that there are both stopwatch and timer options.
Edit: I just looked at the manual for the FR 35 and I didn’t see any mention of either a timer or stopwatch so maybe there isn’t one…
Weird the didn’t include that even on an entry level watch. However, I just looked at my GF’s 245 and it has both stopwatch and timer so I guess that’s where they added those features in the lineup.