I guess that the opening day would be 2019-04-14, Sunday.
https://www.timeanddate.com/calendar/?year=2019&country=26The followings are this year's schedule.
2018-04-15 Sun 9:15- "Yuki no Otani Walk" Opening ceremony
2018-04-15 Sun - 2018-04-27 Fri: Giant Kamakura (Snow Cave)
2018-04-15 Sun - 2018-05-06 Sun: Panorama Road (a promenade on snow between Panorama Plaza and Alps Plaza)
2018-04-15 Sun - 2018-06-22 Fri: Walking Zone (along with snow walls on the bus route and Alps Plaza)
...until late June: Snow Corridor (a shorter pedestrian-only road with snow walls)
2018-05-09 Wed - 2018-05-15 Tue: Giant Snow Maze (at Alps Plaza)
2018-05-18 Fri - 2018-05-29 Tue: Snow slopes #1 (for shredding)
2018-06-01 Fri - 2018-06-22 Fri: Snow slopes #2 (for shredding)
2018-06-01 - 2018-11-10: Gulbe (Lake Kurobe pleasure boat, all the others are at Murodo)
You could get to Alpine Route earlier from Tokyo with Hokuriku Shinkansen. You may consider the directions of mountain slopes. It would be better to climb from the Nagano side in the morning to see the slopes facing the sun. Or, climb from the Toyama side in the afternoon. The choice depends on your hotel locations and your route and pace over the Alpine Route.
Based on tour itineraries by View Travel Service of JR East, I think of these:
2N3D: A later start to view the Toyama slopes facing the sun on D1 and an earlier start to view the Nagano slopes on D3. Full-day activities on D2.
D1: Tokyo to Tateyama via Toyama with Hokuriku Shinkansen, night at Murodo
D2: Activities there, night at Murodo
D3: Murodo to Ogisawa, back to Tokyo via Nagano with Hokuriku Shinkansen
1N2D: An earlier start to view the Nagano slopes facing the sun on D1 and a later start to view Toyama slopes on D2. Half-day activities both on D1 and D2.
D1: Tokyo to Ogisawa via Nagano with Hokuriku Shinkansen, activities and night at Murodo
D2: Activities there, Murodo to Tateyama, back to Tokyo via Toyama with Hokuriku Shinkansen
If you choose an open-jaw flight, the 2N3D works fine with Osaka in and Tokyo out. D1 to be Osaka to Tateyama. The 1N2D with Tokyo in Osaka out. Tateyama to Osaka on D2. The choice should depend on the flight schedule.