I'm kind of new to appinventor, so sorry if I'm a bit ignorant. I've been creating a stopwatch app (Moderator removed the link to your Project on the Designer... no one except MIT and you can access the Project there) and it keeps crashing in the companion app. I think it might be because my phone isn't that new and can't handle the clock because when I increase the clock interval the app lasts longer before crashing.
Is that all your Blocks Ray? We need to see the settings for the Clock Timer.
Also, Clock Timers on Android are low priority, so calculating hours, minutes, seconds as you are now is going to become inaccurate over time (no pun intended).
'Timer Always Fires' is for those Apps that need a timer to continue even when they are off-screen, which probably does not apply to your App. Why did you choose a 30 millisecond time interval?
Best to follow SteveJG's advice and do a search for Stop Watch (might be examples in the Gallery too) to see how to code one accurately.
I think the crash occurs because the Clock Timer Block (+ procedure) has not finished processing before it is called again.
Edit: Actually, since your timer can get into hours, 'Timer Always Fires' is appropriate.