Ok, so now I just use the original script, but added a timer on every join in the list:

.timer 1 5 join #chan1
.timer 1 10 join #chan2
.timer 1 20 join #chan3
---some more here---
.timer 1 180 join #chan19

Would have expected there was a more slick way to do this, but I guess this also solves the problem.