From the details in your post, it sounds like the garden has been a long time in the planning? Could you not have informed him earlier when he was about, rather than wait until you are at a time critical point of the work?
You mention that you want to inform him/ask if he has any issues. What will you do if he objects? Presumably you are going to get rid of the hedge anyway?
I would be cheesed off if my neighbour just ripped up a hedge that bounds our garden without at least informing me, even if it is their legal boundary.
Being as he is not around to inform, I would drop a note through the door explaining what you are planning on doing and perhaps apologising that you have not been able to speak to him face to face about it in advance. Explain that you will try to keep disruption to a minimum & will clear up any disruption to his garden that occurs once the work is done. It will show that you are not just doing it without considering ‘the neighbours’.
Oh, and as above – the birds are starting to get frisky this time of year so look out for nests.