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Had the same problem a few months back. The only thing at Hellifield is the station cafe, and trying to find opening times on the internet is nigh on impossible. No pubs or anything else in village that I could see.
Long Preston does have pubs in the village, which according to Google Maps is about a 10 minute walk, so might be possible to have a meal if you're quick enough. I was planning on doing this until I realised that the Sunday only trains that go direct to Clitheroe from Hellifield don't stop at Long Preston, so instead had to go to Skipton instead.
Depending on which way you are travelling, and if you are getting the Morecambe - Leeds service, it might be possible to get off at Giggleswick and walk to Settle, where there is much more choice.
I made it to Hellifield once and couldn't find much in the way of pubs. Unless you've a way of checking whether the buffet's open, it sounds like Long Preston is the better option (though I've not stopped off there myself). Settle, I have visited and it has some very nice hostelries.