Given that all the other sides in the Division play on a Sunday, London Broncos are between a rock and a hard place on this one. Play home matches on Saturdays and you are imposing a day less turnaround on yourself after an away Sunday fixture (but if you think about it you'd give yourself an extra days recovery/preparation for the next away game!) and that is one of two reasons given for Sunday fixtures on the club website.
Everyone has their own reasons for preferring one day over the other.
Saturday makes a lot of sense to me for many personal and practical reasons. I will certainly get to a few Sunday games next year, but Car hire or Car ownership will be the only way to get there and back with family as it would not be achieveable using rail on a Sunday.
For the Club, they have to work out their market and who they want to attract to the Hive next year and in the future as they are going to be at this level for the foreseeable future. They clearly need to attract an audience locally or at least from a radius around the London area who have no issues about what day of the weekend they play due to travel.
Go Broncos!!