You should leave it for 24 hours with paper towels to check all the fittings and connections, if after a 24h run there are no leaks, you have a big chance that leaks won't be there never if your elements don't break.
Besides that, running it for several hours on the first tests it's almost imperative, all the air possibly stuck on rads and blocks should end on the res ... and maybe that's a 3-5 days task by itself ... or 1-2 days if you help shaking the rads a bit while loop is running.
I had also a drop leak on the first W/C loop i mounted, it was just happening cause i didn't screw hard one of the nuts, once done ... no problems, you're gonna love the water performance, for sure.
edit: if possible, turn the pump to the other side, that way the res-pump tube will be shorter and will give you more flow and pressure, hose management it's also as important as cable management
Did you consider to mount the loop res>pump>block>rad>res also? On single-block loops i read the performance is better since you want the "highest flow point" on your block, give it a try and test which way is better