When you set an alarm on HTC 10, you just get to set the time, repeat and vibration. But to set and change snooze time on HTC 10 for you alarms, do as follows:
1. Open the Clock app on your HTC 10
2. Go to the Alarms tab
3. Use the Add button on the top to create a new alarm (if there is not existing alarm)
4. Tap the 3-dot icon on the top right side of the screen and go to the Settings.
5. Touch the Snooze Duration option and select the snooze duration time from 5 minutes to 30 minutes.
Note that, using the stock clock app on HTC 10, you don't have the option to change the number of total snoozes and change the snooze time for each alarm separately.