It's most likely a string that could be retrieved with an SNMP Custom String sensor, though there are no further processing functionalities, at least for what you're trying to do like "Treat it as a date and compare it to the current date". Might be possible with a custom script that does the actual compare and only reports back to PRTG whether it's fine or not, I have unfortunately to "blueprint" for such a script that I could provide.
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