Protect the international crossing from mountain delay
Spend two full days in Tbilisi, two nights in Stepantsminda and return to Tbilisi before continuing to Armenia. Do not attach the international train or coach directly to the normal mountain-road arrival. Weather or traffic can remove the connection.
Use the overnight Tbilisi to Yerevan train when its operating day and berth suit, or a clearly ticketed daytime coach. Confirm documents, the border procedure and the exact Yerevan arrival. The route does not use the closed Armenia-Azerbaijan border.
Keep the Armenia half selective
Give Yerevan a full day, choose either Lake Sevan or Garni and Geghard, then make Gyumri a day trip only when both rail or road directions leave useful time. An overnight in Gyumri requires an extra day and is better than a rushed return.
Arrange luggage storage for the Stepantsminda return and keep the international departure separate from the mountain road. In Yerevan, one stable base works for both road outings and the Gyumri day. The route is much easier when each border and station transfer is treated as part of the day, not hidden between activities.
With eight days, remove Stepantsminda or Gyumri. With seven, choose one country. The example total excludes private drivers, sleeper supplements, airport travel and border-related changes.