Good lord! My games only last a maximum of three hours. To be honest, this is due to time constraints at the club (we have to clear out by noon) but also I find that the slow games that I played in the dim days of my youth, tend to drag on miserably. The gradually losing side experiences a slow crushing of the spirit as the hours glumly pile on, whereas the winning side rarely ever experiences the end of the scenario as the losing side generally concedes long before the victory conditions are met.
Admittedly that might be because the rules we used in those days were dreadfully slow and boring. There was one massive game we played (that I quite honestly cannot recall the rules nor even the period!) but the there was so little player interaction that one side actually began playing a little board game when it was the other side's turn!
I also quite enjoy painting most times. For me, the drudgery in wargaming tends to be the prep involved in some rules. Rosters, labels, making up an army list – that's what I dislike in gaming.
That said, I do quite like campaigns, in spite of the bookkeeping involved for most campaigns, even though naturally I avoid anything like Tony Bath's detailed rules! Mustafa's various campaign systems, or the Chain of Command pint sized campaigns work for me. I guess in a way campaigns are a bit like your much longer, detailed planning sessions.
If that is the case, I might spend perhaps an hour making up labels for the Blucher rules, or perhaps ten minutes for CoC campaigns to select my supports. For DBA campaigns, map moves take about ten minutes or so for the group to set up our next battles.
I suppose if it doesn't involve miniatures, then my attention span is horribly limited!