ASP usually shows up the first few days of July. If you're paying attention and your admin office isn't screwed up, your ASP letter and endorsement can be done well in advance.
It looks like you mean ISP when you write VSP. ISP should be paid 1 October, but it is often (usually) late.
These special pays are not related to your twice-per-month regular paychecks. They'll appear on your monthly LES, but they are paid separately and can show up on any day. No earlier than 1 July for ASP or 1 October for ISP. (For most of us. There are exceptions for people who graduate residency off cycle, or who renegotiate ISP dates because of fellowship.)