Hi KH3PP3125, someone on another forum told me it would be fine to apply with the 6 paychecks + bank statements, so I applied on April 30 and my husband completed 6 months on May 1. I am really really nervous about this, and my advice would be to listen to everyone here and wait to apply. I'm anticipating a refusal for this and a couple of other reasons, so I'll wait to reapply in September. Is that an option for you? You'll save time that way. However, if you can hold off on the birthday deadline, I'd say apply when he completes 6 months.
I wish they made concessions for parents AND spouses of British kids, my eldest was born in the UK!