Generally speaking, it is after an adventure, during "down time" in an inn. However, if something appears immediately usable (magic sword etc.), then we generally determine ownership more or less on-the-spot.
If we find something someone can use then and there, that person will get to use it on loan from the party for the nonce. We don't do proper division until we get back to town and can get things ID'ed, sold for gold, etc.; just because you're temporarily using a found item doesn't mean you own it (though of course you can put in a claim for it during division).
Generally speaking, it is after an adventure, during "down time" in an inn. However, if something appears immediately usable (magic sword etc.), then we generally determine ownership more or less on-the-spot.
Immediately usable stuff goes immediately to use (weapons & armor and potions constitute the majority of this group), others are identified when there is suitable downtime to identify them.
We split it when we reach homebase - where the PCs can buy and sell loot; but usually in between sessions or at the beginning of the session. Rarely, certain items would be used as soon as they are found and be properly "divided" later; this applies mostly to things loke scrolls, wands with identifications, and so on.
The group currently has a bag of holding. Anything that isn't immediately useful and or identifiable to the party generally goes into the bag to be split at a later time (normally when they are safe in a city or something like that). If the party knows what an item does then it is generally given to the person who would be able to use it best. Treasure such as gold and gems is sometimes split immediately, other times it is put with the group loot to split at a later date or to go towards identify spells, etc.,
If it is stuff that can be used effectively by party members that gets dished out straight away on a 'loan' like basis.
Then when we get to a town with a sizeable GP Limit, we sell stuff no one wants (we get a fixed 80% market price on magic items, 50% on mundane) then dish out the treasure. Then players that want to keep their loan items pay (80% market value or 50% for mundane) into a pot that is then shared out between everyone again, then we go shopping.
Healing items, and other items that have a party utility, this rule doesn't apply. And on really expensive items that we need to keep we just ignore these rules.