Liam,
I was driving through Louth, Meath, Kildare and Offally last week and I saw a lot of OSR that was already fully in flower and still more that was just starting to bloom. Given that you are 'a bit' further South it may well be the case that OSR in your locality is a week or two ahead.
I know a County Down farmer who grows a lot of OSR and whilst normally he would have four or five beekeepers bring bees to his OSR, none of them have been in contact with him so far this year: they (and others) have been caught out by how early OSR has come into bloom in many areas. The fields you plan to bring your bees to - how far out in bloom are they? Are we talking about 10% or 20% coverage of the field?