Give or take, how long do you wait to receive your coins? At what point do you start to become suspicious?
Which coin are you talking about? With ETH, it takes less than 60 seconds. On the other hand, for Bitcoin it can take anywhere from 30 minutes to 3 days, depending on the transaction fee used and the network load. Other currencies such as LTC, BCH, BSD and XLM comes somewhere in between these two.