Due to the change in their flight plan caused by the six-hour delay, the crew had to reprogram a great deal of their onboard data, and this had to be done before they had LOS.
In the event of a secondary control system failure in the engine, the mission rules stated the entire landing phase of the mission would have to be terminated.
“Unlike the roller-coaster ride of Earth orbit, we are entering a slow-motion domain where time and distance seem to have more meaning than speed.” Mike Collins
It looked like they had a leak from one of the propellant tanks on the Lunar Module. If so, that meant abort!