The main goal here would be to reduce the amount of time per turn to a number much lower than 30s, so that players can not wait 29s per turn to play.There is a poker app that I have used that has a "time bank". You have a constant N seconds per turn, and after your standard time runs out you use time from your time bank. It works very well by allowing you extra time to think, up to a certain amount. You never run out of your standard 30 seconds per turn, only your extra time.
The main thought here should be: How many seconds am I willing to wait per player every turn? For me, the answer is way lower than 30s.
A number like 5s here and an appropriate time in the bank would be good.