I would think by now you’d see the pleco taking some food, but some fish can be picky eaters!
My bristlenose didn’t really eat anything for the first couple days either. They more or less were just getting used to their new territory and finding safe places to hang out. Once they got settled in they started to scavenge around and would go for the food before the fish got at it.
Once they’ve scavenged anything from the tank that they’re able to eat, there’s no choice but to start eating the food you supply or they’ll starve. So I think it’s pretty safe to say, if they’re hungry the fish will eat!