I meant the monthly stipend after the initial deposit of credits. I finally figured out that it's monthly based on the date you first subscribed. Derp! Thanks, all.
As said above, once you complete payment (debit/credit) the credits, votes, and stones are given to you immediately.
Make sure to sign up for the free month in the beta first so you get the 50 free ones from there too! :D
If you already have a subscription you can go to this link to see when your next "deposit" will be: http://beta.glitch.com/account/subscription/
I highly recommend that anyone interested in purchasing a subscription do so as early as possible since your stipend allotments start immediately but your time does not start counting down until launch. I just got my third allotment so that means my subscription has already paid for at least 15 months of Glitch.