[NoOne]

when you add the league in creation process, check start date in options for the schedule portion.. the one that's the earliest is what you want. i don't know offhand as i never activate these other leagues.

add all, cehck start dat under schedule options, then delete what's not needed...

i'd actually recommend saving a template before you add those leagues, then start over by reloading your template.. jsut in case it leaves players behind? not sure.. but use a template to "restart' at exact point before you added any leaugeu, then add the one you need.

can delete it and it's players after you start too... that won't change the date at that point and no slow-down.

other option.. start "1 year early", sim to next "march 1" or preseason etc.. then clear stats/history if fictional and you are starting fresh at the date of your choice. probably not an option if using real players... this will add a year of fictional stats to their history etc and deleting history isn't likely a viable choice either.