Where in the NSX UI would an administrator set the time attribute for a time-based...

According to the VMware documentation1, the clock icon appears on the firewall policy section that you want to have a time window. By clicking the clock icon, you can create or select a time window that applies to all the rules in that policy section. The other options are incorrect because they either do not exist or are not related to the time-based rule feature. There is no option to set a time-based rule in the rule itself, as it is a policy-level setting. There is also an option to set a time-based rule in the NSX UI, so it does not require using the command line interface.

https://docs.vmware.com/en/VMware-NSX/4.1/administration/GUID-8572496E-A60E-48C3-A016-4A081AC80BE7.html