This is overkill for your example 1, but the apple watch has an inactivity tracker. It reminds you to get up and stand for a minute every hour if it notices you aren't moving. I've found it useful when I'm sitting around or working at a computer for long stretches.

For your time to stop alert, the only thing I've found that helps is throwing everything on my outlook calendar - it gives alerts 15 minutes in advance of the appointment and that's enough to make me realize that some task is coming up and I need to prepare for it.

I don't think I've seen an app per se that does exactly what you want