The reason for the timer is to account for there being a load across the battery. If the charge controller relies on current only it will never detect end of charge because it will see the load's draw.
Absorption charging is more of a lead acid thing. Lead acid batteries quickly come up to 60% or so charge but then the charge current falls off and the climb to full charge is a slow one. The voltage is raised and current monitored to bring the battery to fully charged much more rapidly at the expense of splitting the water in the cell. Sealed batteries have recombiners to recover the water but only at a low rate. Excessive time in absorption charging will ruin a sealed battery.
The important factors for a lithium cell is to not raise its voltage above the maximum spec and to keep charging current within the spec too. Leaving a lithium battery at the typical lead acid absorption charging voltage won't cause it a problem as the current will taper down to 0 once the battery is charged and unlike lead acid the lifepo4 battery does not have a midpoint where it suddenly becomes harder to charge.
Victron's more recent firmware no longer monitors charge current to see if a lifepo4 is charged instead just leaving the battery at the higher charge voltage for a number of hours (4?) before dropping down to float.