Is it safe to use a wet MagSafe 3 connector after drying for 72 hours?

I doubt it, not the logic board anyway, just bear in mind there can be hidden damage that may have already occurred. I am only pointing that out in an abundance of caution, as well as the fact it's quite impossible for anyone on this site to provide absolute assurance of anything.

Technically speaking the MagSafe port is an assembly separate from the logic board, and is replaceable at a reasonable cost. If you remain concerned, yes, keep using the USB-C power adapter to charge your Mac, and if you are so concerned it might be worth having Apple evaluate it. They may or may not identify liquid damage... and if they find evidence of liquid intrusion they tend to be alarmist about it. So, they may also give you an answer you don't want to hear, even if your Mac is working perfectly.

If you are not already in the habit of backing up your Mac, take the event as a hint: Back up your files with Time Machine on Mac - Apple Support. That just goes without saying, even if your Mac didn't suffer any damage at all. Any device can fail at any time, or for no apparent reason at all.

Here is an older Discussion with a detailed picture of a damaged MagSafe 3 port: Macbook Pro M3 magsafe charger pins burnt and wont charge - Apple Community. If yours looks like that, don't use it. Get it fixed.

Does the Mac operate normally?

The reason for asking is that liquid intrusion is likely to have affected more than what can be seen. Plug it in. It will either work, or it won't. If it does not work, repairs are likely to be economically unjustified.

In an abundance of caution don't leave it unsupervised until you are reasonably assured there won't be any sparks or smoke. Don't place the Mac on anything likely to suffer damage by excessive heat or fire. If the MagSafe connector LED illuminates as expected, the Mac's battery icon indicates it is charging, and all indications are otherwise normal you dodged a bullet.

For reference: Charge your MacBook Air or MacBook Pro - Apple Support

There is a small always-on power supply in MacBook Pro power adapters, so that it can run some logic to decide what it should be doing about supplying main power.

This means that there may be some very small arcing on a perfectly normal, properly working, power adapter at the instant it is inserted into the wall socket. Provided it is only momentary, that is not considered an alarming event.