I think 150 points was the biggest squad size we've done, and that took several hours to complete (2.5ish). Just due to the number of ships you need to move each turn I would expect to spend the better part of the afternoon if you play to total destruction of one side. Sounds fun tho,
Similar experience here. I generally prefer several shorter matches to one big match, especially if the conclusion seems inevitable after a critical turn. But if you want to try it out, I couldn't imagine a better time.
May the Fourth be with you!