So, while you can use Global Libraries, the things you might want to do in them can quickly become rather complex.
I was thinking more about your issue. The issue you are likely having is as follows:
1. You are in Activity #1 when the time matches to 3:55. You begin schedule or execute of the actionlist.
2. The actionlist then causes a jump to another activity which relaunches your timer via your Global Library running in Activity #2. Your script then immediately sees the time match. Result: You have the error about currently executing actionlist.
One way you could solve this would be through the use of System Globals as the Pronto can maintain state across activities only by using them. You'd need to keep 'state' across activities and prevent the time from running except for only 2 times per day irrespective of the activity.
I'm not in a position to write this code as I'm not aware of all your use cases and the complexity of such a solution.
By complexity, I mean 1. There are 2 activities involved and this makes it harder to save state as you move around.
2. There is no way to modify a System Global via an actionlist (i.e. when actionlist is complete, set or clear a System Global that would allow your timer to continue execution). To do something like that, the last action in your list would have to be a Jump to a page and this page would have to have the Page Script to clean up the global.
