Off season training plans

Plan to use a Zwift training plan to kick off the winter for IM training and thinking of the Grand Fondo plan in addition to my running, swimming and strength training (don’t want any more than 4 bike sessions per week, but ideally 3 would be better). The plan states 5-8 weeks but this may extend by at least a week or two due to training. Does anyone know if you can extend the plan?