It's not the current one, but gives you an idea. This is the Brighton Link at Cambridge. The Maidstone Link (who may one day route learn Maidstone!) for the same period had 25 Saturdays off in a 50 week roster.
Welwyn Garden City has a similar pattern of a long weekend off every four weeks, with the previous week usually a random weekday and the Saturday as rest days.
The original plan was for the current one link at Welwyn Garden City will be split into an Inner Suburban (class 717s Moorgate to Welwyn/Hertford/Stevenage) and Outer Suburban (700s Kings Cross to Cambridge, and eventually to Maidstone), but I'm not sure when that is to be implemented.
Expect more Saturdays at work than this in the future, as the service is to be increased on weekends at some point.
'SP' on the roster means Spare or As Required, and means you can be allocated a turn of duty that starts upto two hours earlier or two hours later than the SP book on time. If the turn is shorter than the SP hours, you don't lose out, longer and you get overtime.
You can swap turns of duty as long as both of you have 12 hours rest between duties, and both sign the route and traction. Some people swap for earlies all the time with someone who does lates all the time. People wanting earlies are more common than people wanting lates.
Time + 15% +£50 for working a rest day.
Time + 55% for working a Sunday (outside the working week).
You must commit to working 12 Sundays a year (3 per quarter), although you can give any of these away to someone else who will then take on the commitment for that day - or you can take on the commitment for someone else's Sunday if you want to. This would be in addition to your 12, if you did take on someone else's committed Sundays.
24 days leave (20 would be as annual leave weeks [two weeks together in summer] - although you can float one week and convert into 4 ad-hoc days)
8 Bank holdays, or days in lieu resulting from them being rest days, or working them. If you work one, as well as the day in lieu you get an additional 15% for time worked.