Sounds like you have a YouView box where the NowTV App provides on demand movies only with no live Sky Cinema channels
Based on what happend last year ( if my memory serves me right) the Oscars was broadcasted live first on the live Sky Cinema Channel dedicated to the Oscars (which doesn't help you with a YouView box) then there was a repeat in the evening again on the live Sky Cinema Oscar channel.
So if you want to watch it live in real time from start to finish then a YouView box will not be suitable and you may have to look at other nowtv supported devices.
Then i know for about 7 days the Oscars was added to NowTV catch up using a Entertainment Pass (again no help to you using a YouView box) and i can't remember to be honest if there was also an option for 7 day catch up using a Cinema Pass.
Also i can't remember if the 7 day catch up was the full Oscars event or a water down highlights version of the Oscars lasting about 2 hours.
Hopefully somebody from the NowTV Team can help answering your question in full ?