Why would the travel time Lviv - Mostichka be more than 60 minutes if there are no calls (stops) en route?
It's an around 80 km distance and the train should be running at 100 km/h.
Moreover, a train of combined overnight wagons from the listed trains could leave Lviv around 6:50 which is both convenient for passengers from Lviv and provides time for maneuvering with the wagons from latest arriving train component (#26).
It will arrive to Przemysl 1:30 - 2:00 later, including both border control procedures. That makes 8:50 Kyiv time at the latest, which is 7:50 central european time.
Perfect for further Polish connections departing between 8 and 9.
It might be 1-2 wagons from the Kyiv - Lviv (#91, arr. 6:00), 1-2 wagons from the Kyiv - Frankivsk/Vorokhta (#143, arr. 6:10), 1-2 wagons from the Kyiv - Uzhhorod (#81, arr. 6:20) or 1-2 wagons from the Odesa - Lviv (#26, arr. 6:33).