I spoke to HR today and they told me that I can't go back early if I feel ready early because they have to contract someone to replace me. So I have had to alter my leave form NOW and it should be fine. It's just a matter of whether or not the manager will sign off on it. So I have requested until July and if I want to extend it then I can. Apparently it is easier to extend a contract than shorten one. Oh well.... at least I found out now and not after I went on leave! And thank goodness they haven't started recruiting yet!