13 hour flight with 18 month old and adjusting to 9 hr time difference (UK to Japan)

We are in a unique position of having free flights to Japan if we use them by the end of this year. We live in the UK, so it is a 13-14 hour flight, plus a 9 hour time difference when we land.

This is both mine and my partner's dream holiday destination, however we will also have our little one with us who will be around 18 months old (if we go in September as planned).

We are hoping to go for two weeks, but our main worries are around the 13 hour flight (not sure on flight timings yet), and the time difference when we get there (9 hours ahead). He's only 9 months old now, so it's hard to plan that far ahead knowing how quickly their schedules change with age, and never having had an 18 month old before.

Has anyone had any experience with a similar trip or time difference and can advise on if it's a good idea, or if we should just abort the idea altogether please?

(Worth noting this free flight is a one-off, we wouldn't be able to get it again when our baby is older in future years).

TIA