Lighting and atmosphere
The square and the surrounding streets are lit, so it is easy to orient yourself after dark.
In the evening the square is active with people and traffic, which adds to the sense of safety.
Safety
As in any city centre, keep an eye on your belongings and avoid empty streets at night.
The narrow streets of Old Tbilisi are quieter in the evening — continue along lit streets rather than side alleys.
Getting back
The metro runs until late evening, but in the small hours a taxi is the better option.
Taxi apps show the price up front, which makes them the calmer choice at night.