There are two ways that casinos make money off of poker games. The first way is via the rake, which is very common in lower stakes limit games as well as in some no-limit games. The other way is via a time charge, which is more common in higher stakes limit games as well as in no-limit games at all levels. In a time-charge game, players will each put out a particular amount at each dealer change. This money is then collected by the incoming dealer and dropped down the rake chute. There is no further money removed from the game for the entire dealer down.
If the house allows it, and the players agree, they may use a "time pot" to pay the time charge. Rather than each player putting out a set amount for the down, the money to pay time for all the players is taken from one or two pots. Often the time pot will be the first pot, or first two pots, after the down starts, however they may be qualifying conditions that contribute to the time being taken from a pot later in the down. One such qualifier is the pot size; that is, the time charge may not be taken until the pot is large enough to pay the entire charge. This type of time payment is thought to benefit the tight player as they will be playing fewer pots and, thus, may avoid paying time more easily.
Because most cardrooms are unwilling to wait for the first qualifying pot to accept payment for time, one player will often post time for the table, expecting to be reimbursed out of the first one or two qualifying pots.