Hi, @flarebright,
I confirmed Heker’s spawn rate in single player to be 60-75 mins; you need to wait for him or go into admin mode, enter the command “slowmo 100” to speed things up. To set it back to normal speed, enter the command “slowmo 1”. Otherwise, you will need to wait 4 respawns of the camp to get him. I have got him 6 times now, on both of the servers I play on.