If you run it as a subscription they bill you the last thursday of the month for the next month's sub. Then once it is announced on the first day of the month you get access to the early release games immediately. (in this case HI4, Blackwake and Portal Knight) and then the rest of the previous month's games unlock (on the first as well).

So looking at last month's sub which was June's Humble Monthly.

April 26: Autobill for June's Monthly Bundle
May 1: The Rest of May's Games were announced and Released
May 1: June's Early Access Game was Announced and was playable (Destiny 2)
May 28: July's Bundle Autobill
June 1: Rest of June's Games were Announced and Released (Styx, Yooka-Laylee, Cook, serve, delicious 2, Pillars of Earth, Bear with me, suguri 2 and subserial network)
June 1: July's Early Access Games were announced and playable (Blackwake, HOI4, Portal Knight)

It's really confusing as to when you pay for which month and when you get what month's games. But if you bought a whole year you dont have to worry about much of that mbeaver.

Keep in mind though that they accounce the main unlock games on the 1st but you wont unlock until the 5th unless you unlock them manually. So if you bought a year and they announce games you dont care about you can "pause" your subscription before the 5th and save that month for a game you want. Or you can unlock right away and play.

https://support.humblebundle.com/hc/en-us/articles/210560328-Humble-Monthly-FAQ