Is there a regulation for medical TDY?

It depends on a couple of things. First being how far away is the appointment. Second is what time is the appointment. If it's close enough that they can make formation and arrive at their appointment without rushing 20 - 30 minutes early than I say yes. If it's going to interfere with what I just stated than I would have them call in when they arrive at their appointment that way you're sure that they arrived. That's how I have done it in the past.

Ok. For arguments sake, let's say you are ordered to appear for medical appointments as given by your provider(s) office(s). And let's say your appointments are all on the same base.....since you said just for one day. Your appointed place of duty is that/those appointment(s), yes.....but depending on when that first appointment is....I would have you at first formation for accountability purposes, then release you for your medical events.....then have you report back to me at the end of all your appointments for that day for accountability and to track if you have been given any other appointments.

Medical TDY?

"Medical TDY" is typically done as an accountability measure..specifically BECAUSE the appointment will have the service member away from the unit at normal accountability times, or farther away in distance than would be normal for a standard duty day. Occasionally when real cost is inured by the military member for travel or lodging, those costs are authorized and approved using TDY.

Strictly answering your question...It depends... If first formation is 0730: You medical appointment is at 09:30 at a provider 30 miles off post, with a common travel time of 20 min.... Yes, I'd have you show at first formation..

Same situation, but its now snowing, and typical travel time is more than an hour...I would not have you show for first formation, but I would direct you to call your 1st line supervisor and inform you arrived at your place of appointment on time and safely.

In example:
If your stationed in Fort Wainwright AK, and need a test or procedure done at Fort Richardson hospital... I would (did) have the commander sign a TDY authorization for that member.
No matter if they are going down by POV, TMP or taking the fixed wing hop.

Same for a 0700 appointment in "town" with possibility you may not return to your assigned place of duty that same duty day (say going to a drug treatment facility appointment in town, and one of the possible outcomes is inpatient treatment)

Your regulation source is the Joint Federal Travel Regulations/Joint
Travel Regulations (JFTR/JTR) as Travel Under Special Circumstances or Categories
http://www.defensetravel.dod.mil/Training/DTS/Docs/TrnMat/DP_11.pdf

And local business rules.. Check with your DTS clerk


MEDIC MIL MEMBER
TDY
Transfer of patient to/ from medical facility or home under TDY An active duty member patient, ordered to travel for necessary medical care, is authorized the travel and transportation allowances for either TDY or PCS, as applicable.

Advances may be made against such allowances to the attendant/escort. Advances must be made in accordance with Service instructions. An active duty member patient, ordered to travel for
necessary medical care, is authorized the travel and transportation allowances for either TDY or PCS, as
applicable.

Advances may be made against such allowances to the attendant/escort. Advances must be
made in accordance with Service instructions.

When transportation-in-kind is furnished the member patient and attendant/escort must be furnished enclosed room accommodations when required under Service regulations. For more information see JFTR, Chapter 7, par. U7252.

I'm not sure how you would show up for formations, you'll be on TDY, not with your unit. The most important thing to remember with medical TDY is to make sure you are approved in DTS prior to leaving. Once you travel to your appointment, it's difficult to get those orders approved retroactive. Also, your government travel card is authorized so use it. Don't come out of pocket for hotel expenses. This protects you in two ways: first, you aren't going into debt or financial troubles paying for your expenses; second, if there is a balance on your GTC because you weren't properly reimbursed, your leadership has more of an urgency in helping you resolve it because delinquencies are reported higher.

I can't speak for the army, but in the Marine Corps if there are light duty Marines, it depends on the restrictions and command discretion. The thing is that medical chits are not orders. In other words, neither you nor your command has to obey them. Although if forced to go against the chit, whom even had given that order is now able to be under scrutiny. Usually the command follows the chit or it doesn't matter anyway though. If that service member disobeys the chit he/she can be charged with malingering.

It all just depends on the situation and the command, and the service member (reputation).

If your appointment is on the same base and is not at the same time of pt formation(which in most places I have been there are no medical appointments at those times) take your happy ass to formation and then go to your appointment. If your formation is at a different place, then I am sure your NCO will report you in formation as accounted for.