startup timeout after a certain amount of simultaneous jobs

I have some services which can be scheduled in pg_cron at the same time to be executed in a queue.
The function runs a shell script which does some file copy operations on fileservers; the amount of data can be up to some GB and thus take a while. Until now (over two years), this setting worked fine also when there were big amounts of data and thus the next job in the queue starting with a very long delay (once there were about 40 minutes).
Yersterday, I had first time 36 simultaneous jobs, four of them failed with "startup timeout" message, they started about 5 minutes later.
I recently upgraded pg_cron to postgresql-12-cron 1.5.2-1.pgdg110+1 (debian bullseye).
Can I get an information about the conditions of this startup timeout? Can I influence it?
Thank you in advance for an explanation,
Best, Elke