Ticket Advice?

I’m trying to understand the change rules and which tickets are best to buy. Trying to keep myself from overbuying…
We’re doing a split stay between Universal and Disney. Might also go to Sea World for a day.
I think I want to buy 7-day Park hoppers. Disney will be at the end of our trip. But, it’s possible we’ll go to MK on the day we arrive because 1) I like to start and end at Magic Kingdom and 2) Magic Kingdom is open latest, giving us more time if we arrive later in the day.
If we do Disney the 1st day, I need tickets to be valid for 13 days. We won’t decide until that day.
Should I buy 7-day tickets starting on arrival day? Is it easy to move the day to further in our trip after the ticket window has already started? Or, if I buy starting later in the week, can I stop at guest services and add days to the front end of my ticket? Or, should I just pay for the 10-day tickets now? There are 5 of us so the price difference adds up.
Thanks for any advice/opinions.

When is your trip? The main issue I see is if the parks yiu want can be reserved if you make a last minute adjustment.

I don’t think 7-day park hoppers will be good for all 13 days, unfortunately. Undercover Tourist shows that a 7-day Disney ticket is valid for 9 days after the first use. There is also the issue of park reservations and the possibility of being locked out of the day you want if you wait until you get there. Disney hasn’t made it easy for spur of the moment changes.

A 9 day ticket would be valid for thirteen days.

Maybe what will work best is buying 7 days starting for the day we check out of our Universal hotel so I can reserve the days at the end of our trip. I don’t think I’ll get locked out the first day bc the crowd calender is lower at the beginning of the trip. But if you guys think I should buy the longer ticket now, I could go for it… just trying to save a bit where I can.

Could you share with us your tentative plan and how long your trip is? If there is a big break in the middle without a planned Disney park day, maybe price check buying a 1 day ticket for the first day to use at MK (or wait for special events to be announced and see if a MK party matches your arrival?) and then dated tickets for the length you need at the end.

I talked it over with DH and we agreed to just have dinner and relax on arrival, or go to Universal if we arrive early. Now I’ll guess which order I want to visit parks and make reservations…