Umberto, a payday in the U.S. is usually one of four options:
1. Bi-monthly (twice a month) paid on usually the 1st of the month and the 15th of the month.
2. Every two weeks, paid usually on a Friday. With this method, you usually get paid twice a month, except for two months out of the year, you get 3 paychecks in a month. (<-- This is how I get paid. My extra paychecks come in July and December this year.) This is just due to how it works out with 5 Fridays in the month and the first check coming on the 1st of the month, the 2nd on the third week, and the 3rd on the fifth week. The Friday you get paid varies by the company, as well. As in, this Friday is not my payday, but it is my girlfriend's payday.
3. Weekly, again usually paid on a Friday, but not uncommon for the day to be a Thursday or even a Wednesday (or maybe some other day). Usually weekly paid jobs are those who work as temps and in places like fast food, etc...
4. Monthly. In a lot of government jobs, monthly pay is an option. You can choose to to receive it all in one payment if you do it this way, or elect to receive it twice a month, in which you'll receive half a payment on the 1st, and the other half on the 15th.
As you can see, there's nothing standard about it, lol. I guess if you're trying to take payday into account, it'd be best to release on a Friday (definitely), possibly around the beginning or middle of the month. That'd probably suit almost everybody.