Use Grand Central Dispatch to schedule a function same time every day

Question

I have read this answer and I do not believe it has what I am looking for but I a am beginner and I am happy to have someone point out the answer in this link : dispatch_after -

Answer 1

Importantly, you should use dispatch_walltime instead of dispatch_time. The difference: If you set a dispatch_time for "1000 seconds from now" it will run 1000 seconds from now (if your app is running). But dispatch_walltime will calculate which time that is on the user's clock, and will run when the user's clock reaches that time.

So if you set up dispatch_time for 9am tomorrow morning, and I set the clock on my device forwards by five minutes, then dispatch_time will run when my clock displays 9:05am. dispatch_walltime will run at 9:00am. (You'll have to experiment what happens if I change the clock from 8:55am to 9:05am because then running when the clock shows 9:00am is obviously impossible).