I have and now it’s timing out even though it’s got a good 15 minutes to build them which was plenty before
See my answer to your other post regarding the plan limit:
Just because you mention “minutes to build”:
The scheduling interval has nothing to do with the environment creation.
When the scheduler starts, it first ensures that all environments are created.
For each environment, you can define an Environment build timeout (default: 10 min).
After this phase, the scheduler starts the execution phase.
If a re-creation of environments is needed, you need to restart the agent.
I hope that clears things a little bit up 
Regards, Simon