I get paid every two weeks, and this year August happens to be a three-paycheck month for me. It's also my first month of using YNAB. I'm in pretty good financial shape overall so I just assumed I already had enough for a buffer, but once I set up my budget in YNAB I discovered that I wasn't quite ready to start living on last month's income. But I was able to take advantage of this three-paycheck month to provide a kick-start in the right direction. Here's what I did:
I allocated my first paycheck, which came in early August, to income for September. That made things pretty tight, budget-wise, until my second paycheck arrived in mid-August, so I allocated that paycheck to income for August to get me through the month. My last paycheck arrives on August 31 so I'd have to budget that as income for September regardless. This will allow me to allocate my two paychecks in September as income for October, and I'll be implementing Rule 4 with a full buffer.
The tricky part for me is that my mortgage payments are also every two weeks, on the same day as payday. So while August is good because it is a three-paycheck month, it is also a three-mortgage-payments month.
I'm just tossing this example out there in case it's helpful for anyone who's trying to build up their buffer but finding it hard: if you're paid every two weeks, look in your calendar for any three-paycheck months and put them to use!