of thumb is 7hr from 50% for a reasonably sized charger. For an oversized charger you could shave maybe 1/2hr off. You can up the voltage to shave this down more but seriously compromise the total life of the battery.
Using your example above the charger will put out its max rate of 50amps for 2-2.5hr. This is called bulk charging
voltage will rise slowly from 12.0v to something around 14v.
At the point that the battery reaches the absorption voltage then the charger will start decreasing amperage to keep the charging voltage from exceeding target absorption voltage. Target voltage depends on whether you have FLA, AGM
or Gel batteries
Different chargers use different means of deciding when the battery is at 100%. Some you a simple timer that starts when the battery gets to absorption voltage. Some chargers use charging amperage to decide when 100% is reached. I believe battery makers usually indicate that when charging amps gets to 0.5-1.0% of capacity (C). Using your example above when charging current
drops to 2.5-5.0amps then the battery is pretty much full.
When a charger decides by whatever means that the battery is full then it usually switches to a float voltage of about 13.5v. This counteracts the self discharge of all lead-acid batteries including Gel and AGM
The exact voltages for absorption and float depend on which type of battery you have. In setting up a charger you will need to read the manual to figure out how to set it for the battery type you are using. Don’t mix battery types.