Upon takeoff you will start retracting the gear after - obviously - having rotated.
When initiating the go-around with all engines running you would wait for positive rate before raising the gear, situation not much different.
However in the worst case, you are going around from a OEI situation and you will be retracting the gear while rotating, with extra g-load, that's extra gear weight to be pulled in, and may take longer.
?
jr