I know that Meditations was originally written in Greek, but I'm curious to know how you would write "Confine yourself to the present" in Latin? Thanks.
In the original Greek, your quote is:
περίγραψον τὸ ἐνεστὼς τοῦ χρόνου. (Meditations 7.29)
This literally means: "Circumscribe the present time." (See meaning III.2 of the LSJ entry for ἐνίστημι.)
While it would be simple enough to imagine a Latin equivalent, there is actually already a famous translation by Wilhelm Xylander (or, in German, Holtzman) in the 16th century.
Circumscribe instans tempus.