By default, SCCM collections update once a week. this may or may not be sufficient for your needs. When you create a new Collection in Powershell, you can pass a -RefreshSchedule parameter.
Set-CMUserCollection and Set-CMDeviceCollection accept the -RefreshSchedule parameter though this doesn't appear to be documented anywhere - Google suggests long scripts to do this.
We wanted to set our user collections to update every 4 hours. It proved to be quite simple. First we created a new schedule object
$sched= New-CMSchedule -recurinterval Hours -recurcount 4
Then we passed it to each user collection.
foreach ($x in Get-CMUserCollection){Set-CMUserCollection -name $x.name -RefreshSchedule $sched}
