Day trip from Tokyo to Alpine Route

I am going to Tokyo this May 28. I just would like to know if a day trip from Tokyo to the Alpine Route and back to Tokyo again at the end of the day is possible. Because when I checked hyperdia, the earliest train from Tokyo going to Nagaoka, and then to Toyama, is at 7am.

It is possible. I recommend to start from the Nagano side as follows:

06:24 depart Tokyo by Nagano Shinkansen
08:03 arrive Nagano
08:30 depart Nagano by bus
(https://www.alpico.co.jp/access/express/nagano_omachi/#timetable_summe...)
10:15 arrive Ogizawa

Traverse Alpen Route:
http://www.alpen-route.com/en/wp-content/uploads/2013/02/timetable02.p...

Trains back from Toyama to Tokyo operate until late. The fastest way is by Hakutaka limited express and Joetsu Shinkansen via Echigo-Yuzawa:
http://www.hyperdia.com/

Thanks Uji for that advise. How long do you think would it take for us to go back from Toyama station to Tokyo?

About 3.5 hours. Please use the link I provided to look up connections yourself. Here is the link once more:
http://www.hyperdia.com/