Flying from Tokyo to Kansai Airport

We will be travelling late April/early May from Kyoto to Tokyo via Fuji Five Lakes, then returning to Kansai Airport for our flight home.

We have worked out that it is cheaper to get train and bus tickets and an airfare than to get a JRP.

My question is, if our flight home leaves Kansai at 8.25pm, would a flight from Tokyo arriving at 4.35pm be sufficient to allow for delays/cancellations or should we aim to arrive earlier?

Yes, that is sufficient time.

from Tokyo arriving at 4.35pm be sufficient to allow for delays/cancellations or should we aim to arrive earlier?
Under normal circumstances , yes it willl be enough. But not in case of cancellation. Or any other major distribution. Like for any other kind of transport.

Just make sure you are flying into and out if KIX. ie you donft fly into ITAMI but leave from KIX. (This might sound like a stupid advice and I am sure you arenft stupid but you wouldnft be the first to loose a flight because you were at the wrong airport.

Enjoy your trip to Japan !