iRule to disable a pool to new connections

You can get iCall-like behavior prior to 11.4 using user_alert. Take a look at this thread:

https://devcentral.f5.com/questions/clearing-machine-cache

This will allow you to react to a data plane event (ie. a syslog message) in the management plane (ie. to run a script). You wouldn't want this sort of thing to get triggered on every request as the management plane is not designed with the same capacity as the data plane. Alternatively, if you're simply looking to disable access to the VIP or specific pool members during a certain time of day, you can a data group that defines the up/down times (and other settings) and an iRule that reads this data group on each request.