I recently came across a customer scenario with the following requirement. They wanted that during the day the whole team receives alerts, but that during outside business hours only the person on call receives the alerts. Is this doable with Enterprise Alert?

Yes, this is possible. You can achieve this by creating two alert policies. Here is the general idea.

In one alert policy you address the team during business hours (escalation or broadcast):

In the second alert policy you address the team using the on-call plan outside business hours:

You can define the business hours according to your needs then.