Hi anyadgray,
Totally get why that's a bit confusing. MYOB can be a bit "keen" and start tracking from the start of the financial year. Great question though! Hopefully one of our legends here in the community can jump in and share how they've handled something similar. That said, for something like setting up a long-term liability that only kicks off from April, your best bet is to have a quick chat with your accountant. They'll be able to guide you on the cleanest way to set it up (like using opening balances or journal entries) so your reports stay spot on.
Regards,
Sai