GTV - dependant extending visa but cannot calculate the IHS due partner switching to IRL

[curg]

Hi,
I am wondering about how to calculate the IHS costs in my situation. I am a dependent of a GTV 3-year route visa holder, and my partner is due to start his IRL application next month.
In the meantime I would like to extend my GTV dependent visa for 2 more years to complete the 5 years rule, but on the IHS website, the form requires me to provide an estimated expiry date for my partner's further visa permission. I cannot enter the expiry date on his current visa as it is due to expire in 1.5 months. The IRL application is yet to be started (waiting to fulfil 28 days period). Would it be okay if I put an unverified (estimated) date to cover me for 2 more years and pay the IHS for 2 years? Do I need to wait for my partner to start the IRL process?
Many thanks!

[zimba]

The immigration health surcharge online system is not smart enough to calculate this automatically. ILR has no expiry date. You should enter a date that is 3 years in the future to get a correct IHS calculation. Otherwise, the system will charge you less and the caseworker has to request you to pay the remaining fees, delaying the application.

[curg]

Dear Zimba, Thank you so much for your help!