Look, more than likely, it's just a matter of your location and the location to where the letter was mailed.
For instance, I could mail a letter first class, or, in the larger size Priority envelope early in the day from a mailbox or post office on Pacific Coast Hwy in Malibu, and either one would be delivered halfway across the country to particular Houston or Austin, TX, zip codes on the second day. Same for Vegas to those zip codes. Great postal service, but I had learned where and what time of day the outgoing mail would be most expeditious.
However, the same letter mailed from the same facilities to The Woodlands - just 30 miles north of Houston, would usually take three days - maybe even four days once in a while. Same for a letter from the Houston or Austin zip code to Solana Beach - just 17 miles or so up I-5 north of San Diego.
I could mail a first class letter from the same postal facilities to New York City - including mailing from Houston to NYC - and it would take four days, even five days at times. Mailing a letter from Houston to Conroe - just 35 miles up I-45 north - could easily take three days to be delivered, at times!
If one is mailing the same letter from a more out of the way city or town to any of the cities above, it can easily take another day - especially if the mail leaves your facility only once or twice a day - and longer if mailed to another out of the way location.
And, arrival day can also depend on what day of the week you mailed it. Did it go out on a Friday or Saturday?...
Hope those scenarios helped. After all, you mailed a check, not something of unusual size or weight for the envelope.
