Give or take, how long do you wait to receive your coins?
For btc Depending on the tx fees set i would say not more than an hour, on average its takes 15-30 minutes then for coins like Ethereum anywhere between 30 seconds to 3 minutes depending on on how congested the network is.
At what point do you start to become suspicious?
I get worried about such transactions not suspicious but its being long since I experienced long hours/ days of waiting when using btc, for other alts after an hour I without receiving the coins I get worried.