I'm assuming since I remember having my Ocadoversary voucher around August last year, that Ocado renew 6 monthly as Tesco and Sainsbury's do.
My last £5.99 payment was 4th March, so I'm guessing 3rd April was when the next payment was due, so my pass will be valid until then - which doesn't explain why they increased my pass price from £1.99 to £5.99 in November! They seem to be making up the rules as they go along!
Weirdly, I can see way more slots after 4th April when I'll have to pay for deliveries, than I can for the dates my pass is valid - it seems that while I have my pass I can only book 1 slot per week, but once I have to pay for them I can have as many as I want! Unless the dates available will disappear once I've booked another slot - guess I'll find out once my pass expires, as I do plan on ordering occasionally just for the items I can't get elsewhere.