Hi Rob,
That’s great you are planning ahead.
This is the perfect order of plans: LW Coaching Masters 40+ plans for Cross Country Mountain Bike Base Training Plan, Cross Country Mountain Bike Build, Peak and Race Training Plan prior the to the Mountain Bike 3-4 day Stage Race Plan.
One option is to shift the training plan one day back so day #1 of each week falls on your Sunday instead of the usual Monday. You can strength train (day 1 session) on day 1 (your Sunday) before skiing to stay on plan. On a week where you are skiing both Sat and Sun, drop either the day 6 or day 7 ride and replace with your ski day.
Coach Lynda