To change custody or parenting time (I HATE the term "visitation", as you do not visit with your kids, LOL) requires a change in circumstances. You appear to have that, with his changing work schedule.
Explain it EXACTLY as you have here. You went with HIS days off, in order to give him time with the child (as a shift worker myself, I want to THANK you for considering that he did not have traditional weekends off, good job maam.), but his schedule has changed, and you want to reconsider the schedule. Offer week on/week off, if they refuse, go with standard Every Other Weekend and a mid week visit.
You are being VERY reasonable. I was in a similar situation, my ex was abusive and only got Saturday, from 2 pm to 5 pm. But because it was EVERY weekend, we couldn't go away for the weekend.
Best of luck.
Why give a "senior" discount, they have had plenty of time to raise the money...