The complete loop by road from Kalambaka to Kastraki, up onto the massif to see all the monasteries, and back down to Kalambaka, is just under 20km in length.
If you drive it yourself, it’s just about possible to see all the monasteries that are open within a single day. Plot your route carefully, and start as early as you can; especially in summer, and around Easter, the Meteora fills up with day-trippers from further afield.
Alternatively, a bus makes the circuit three times daily, making several stops along the Kalambaka–Kastraki road (one way/all day €1.80/5.50); check with your accommodation for the current timetable. There's a handy stop near Vrachos Camping. By bus, there’s enough time to see perhaps three monasteries in one day. Many visitors take the bus to the top, then work their way down and around on foot, finishing at either Moni Agiou Nikolaou on the Kastraki side, or at Moni Agias Triados on the Kalambaka side.