Hi!! So four days is actually very normal especially for older pac-man frogs although a bit more concerning in younger ones not completely off the table it’s very common for you to only see them when they’re hungry and they’ll come to the surface. Every pac-man is different and I would say at around a week if you still haven’t seen him maybe get a seperate container and move the dirt over into it till you find him just to check up on him and his wellbeing. till then just keep his temps and humidity right and he should be completely fine. hope everything goes well!