Can anyone give me a quick explanation of "Maximum Credit" in PBS?

I'm thinking of bidding the following in bid group 1:

1. Start Pairings
2. Set Condition Maximum Credit Else Start Next

My question is what will trigger the "else start next"?

ALV is 78, with LCW of 70:30-85:30. What credit threshold does PBS need to build me to, to get a max line?

The reason I ask is I'm in training half the month and can bid reserve and still end up with 76ish hours. If that's all I'm going to get anyways, I'd rather just be on reserve. I don't want to get stuck with a line worth less than 80 hours or so, when I could sit reserve for 76.

Thanks