What are you actually using to detect "presence"? Just whether the multisensor is reporting some attribute (any attribute)? Or do you somehow have the multipurpose sensor able to respond to a magnet and open/closed based on whether you're there? I'm not sure what you mean with your polling idea. It sounds like you want the multisensor to have a clock that can be checked, will sync with the hub, and drift if it doesn't communicate for a while, but it doesn't.
Before I start, I'm not sure this is the best use of that sensor if it's on battery power, as it will probably freak out and go into "panic mode" every time you leave as it tries to find a new repeater or route back to the hub. I'm not sure what effect this actually has in that regard but imagine it's worse than not.
Anyway, if you're just trying to guess presence based on the reporting of other attributes, Rule Machine doesn't have any generic "last activity" kind of trigger, but you could pick a few sacrificial attributes and use them as proxies. Maybe something like:
Multisensor temperature *changes* OR Multisensor acceleration *changes* OR Mutlisensor battery *changes*
Cancel Delayed Actions
Run Custom Action: Virtual Presence Sensor.arrive()
Delay 2:00:00 (cancelable)
Run Custom Action: Virtual Presence Sensor.depart()
I'm making it wait two hours, which unless your garage is climate-controlled should probably be often enough for the sensor to have reported in at least some value once. This is obviously not the fastest way to determine presence, but with a sensor that doesn't send time-based checkins, it's a safer option. With a custom driver, you might be able to configure a specific reporting interval and use a custom app to check for last activity (something like Device Watchdog, which actually does--I'm cheating with RM by looking at whatever attributes I can think of instead), but I haven't seen anyone try that, and there's no native way with Hubitat (or SmartThings) to configure that exactly at the moment, though most Zigbee devices can be customized in such a manner.