If the queue of scheduled map/reduce scripts is created at 11:00 and I manually trigger a map/reduce script with priority “high” at 11:01, will it be executed before or after already queued map/reduce scripts of lower priority?

Each map reduce has multiple instances, one for getInputData, could be multiple for both map and reduce depending on how many processors you've got and then one for summarize. Your job that you submit at 11:01 with "high" will take precedence over any lower priority instance when a processor gets available. It will not shut down existing running jobs.

Ahh okay so even on the instance level, that’s cool! I knew it wouldn’t stop already running instances but I wanted to know how prioritized the high priority scripts are and that was the answer I was hoping for so thank you!