Thanks for that information. I hadn't realised that there were queues sometimes as this has never happened to me before. I did in fact make a deliberate minor punctuation change to the listing this morning and relisted it in the hope that it might then appear but so far no luck. I will do as you suggest and give it 24 hours and if it's still not appeared I suppose I'll have to try to end the listing if I can and the start again from scratch. I hope it doesn't come to that.
Cheers.