According to Catholicism, how long can the main meal during Lent last for?

According to Catholicism, how long can the main meal during Lent last for (time wise)? Most Catholics who fast regularly know how to fast and abstain on fast days, especially during Lent. But, is there some guidance or rule in the writings of Catholic theologians or Canon Law on how long (duration in time) the main meal of a fast is permitted to be? For example, are Catholics permitted to make the unique meal of the day last one, two or perhaps even three hours? Are there any historical references that deal with this subject matter? Naturally we must avoid gluttony even on fast days!