This will be the 24th drawing. The $253.7 million cash value is higher than usual, so the advertised $373 million is about the same value as previous jackpots of about $400 million or more, but the last time PB got to $400 million (advertised at 414 and 251.1 cash on 3/9/19) it was the 21st drawing. The one before that as 470 (268.6 cash) on the 20th drawing. Maybe you weren't watching for a while, but I'd say it's taking it's time to climb back up.
As for when you buy, it doesn't mean a thing. Either the results are preordained or they're not. If they're preordained you'll get the numbers you're supposed to get and they'll match the numbers that are destined to be drawn or not. If the results aren't preordained you get whatever numbers you get, and then later on the winning numbers get drawn and either match the numbers you got or not.