Keep Yerevan as the main base, then slow down in Gyumri
Spend four nights in Yerevan for the city, Garni and Geghard, and Lake Sevan. Travel to Gyumri for two nights and return with a final Yerevan buffer when the flight timing requires it. This gives each road outing its own day and avoids using Gyumri only as a timetable exercise.
For Garni and Geghard, confirm the route, waiting and return. For Lake Sevan, name the actual destination; Sevan town, Sevanavank and other lakeside areas need different final transport. Carry a layer for the higher elevation.
Choose both Gyumri directions together
Use the current South Caucasus Railway information or a clearly confirmed road service. If the return is too early for a useful day, stay overnight rather than forcing a day trip. Keep the final flight separate from an unprotected intercity arrival.
Pick the Yerevan base for the airport route and Sasuntsi David station as well as central walking. In Gyumri, a room near Kumayri gives a better evening than staying only for station convenience, but include the transfer with luggage. Keep the final Yerevan buffer when the flight timing is important.
With five days, remain in Yerevan and choose one road outing. The example total excludes private drivers, airport travel and major admissions.