Most Helpful Guy
I wouldn't look much into it. Depending on people's routines it could very well mean it is the day when they are free.
For example, I could already have plans for Friday. Be hungover on Saturday, sadly Saturday is when I have to do all chores that have piled up over the week (cleaning, gardening, laundry and cook for the next few days) so the remaining day where I can truly "turn off" is Sunday.
For a person with my routine a Sunday lunch/afternoon would be ideal time for a date.