The Express monorail (TTC/MK) runs from an hour before park opening to approximately an hour after park closure. The Resort monorail (the inside loop that stops at CR/Poly/GF) runs from early morning (at least 7am) to late at night (around 11pm) to accommodate resort guests getting to ADR's.
If you are at one of the MK resorts later than MK park hours, you can still get to the TTC if you need to by exiting the resort monorail at Poly and walking to TTC, and then walking to the parking lot if the trams are no longer running. Our experience has been that the resort monorail does not stop at TTC past one hour after Epcot closes, and does not stop at MK past one hour after closing.
You can get some form of bus transport, connecting through DTD, as late as 1 or 2 am, depending on how late DTD is open. If you are relying on Disney transport instead of driving to TTC, you would have to use this route from the MK area once MK transport to the resorts has finished for the night. Since this could take 90 minutes or more, if time is of the essence, you can take a taxi from one of the MK resorts and get back to your resort quickly (although it'll cost you).