If the indecision is an anxiety thing, time limits are the worst approach.30 seconds is an option. It can work. And I would take the bolded a step further, 30 seconds for certain players. Other players don't need it.
I can say this, having implemented the 30 second rule several times, there is a point to it where it no longer creates fun tension, but rather anxious tension, which in my experience, has never been good. It just makes the player that has a hard time deciding or a player that loves to reassess and do the "ultimate" tactic frustrated.
Getting them to realize the don't need to optimize every action, or just that their default action is always good, will work better. Unless the anxiety is really bad, which gets into disability territory.