If the bus reliable?

I would appreciate if if someone can help me with this situation. I have a flight to catch at Narita airport to Chicago at 12 PM (noon). I am thinking to take the night bus "Seisyun Dream" from Osaka at 9.40 PM the previous day, That would allow me to arrive at Shinjuku station, Tokyo around 6AM, And from there I will take a train (express) to Narita. In principle, I should be in Narita around 8 AM. and that will give me enough time to do the check in, and to catch my flight at 12 PM. However, this is the first time I am going to take the bus in Japan and I wonder if the bus is reliable? Normally the plan should work out fine, however I may not foresee some potential problems caused by traffic or delay.

Sorry for such a long message. Many thanks!

In my experience after 5 trips to Japan everything is reliable although I rarely use highway buses. I prefer the train.
There are 4 trains from Shinjuku to Narita airport between 0607 and 0707. Travel time is app. 90'
There is then an hour gap to 0803 arriving 0929.
There is also a train from Osaka at 0034 with connection at Tokyo to arrive Narita at 0837 but I imagine it would cost far more than a bus.