I would like to add that manually choosing spiders from the drop-down list stops working after about 9 spiders or so, so then you have to do it again and make sure you don't pick the same spiders as before. If it kept going until you actually had no spiders remaining, it would be a fair option.
Hello. Any update on this?
The UI uses the API to schedule the jobs, so why not use the API if you need to run multiple spiders?
Alternatively, you can use Periodic Jobs: https://support.scrapinghub.com/support/solutions/articles/22000200419-scheduling-periodic-jobs