I pretty much watch the whole game for every game, though some times I'm multi-tasking and not really paying attention (work, playing on my phone, etc.), but the game is on (overall I'm paying attention more often than I'm not).
Even though I just watched the whole game, I always look up the box score after the game, to see how everybody did on paper, and see if anything slipped past the ol' eye test.
Usually poke around online afterwards (here and both r/nba and r/bostonceltics over on reddit), see what people are saying, get the key quotes from the post game interviews, etc.
I eat my breakfast at my work desk, and while doing so will usually check to see what's trending Celtics related (here and reddit), follow up any of the juicier quotes/highlights to see how people are reacting and
may watch some of the individual highlight reels for the past game that reddit user Timi093 puts together.Then when I want to distract myself from work, I come here and argue about Centers, Moses Malone, random people's Hall of Fame credentials, etc. Spend a lot of time checking random stats at basketball-reference (usually in relation to some argument here). See if any Celtics news is trending, or any new quotes/tidbits came out of practice, etc.
So in summary, I watch just about every game, and check online several times a day for Celtics related news/discussion.