I assume by IF'r you mean intermittent fasting?
I am in no way an IF guru, but I am not sure taking 4ad/decavol would be an issue. Shouldn't be much different than taking in some electrolytes.
I would just dose per the bottles instructions in the am and pm. Spread the 4ad and decavol out by 30 or so minutes to ensure maximal absorption of each, as only so much can be absorbed via the mucosal at one time.
Hope this helps and if I am off in what you were asking just let me know.