If worst comes to the worst with regards to your shifts…. Even though you don’t seem to have difficulties gaining access to your son from his mother; If you can find the cash to just go as far as mediation with a Solicitor (would cost equivalent of maybe 1/2 hours? It is also something she can not refuse to attend – it’s legally mandatory) then your employer is legally bound to allow you the time off for whatever access you have agreed via mediation. It holds as much weight as a court order and by law, employers HAVE to allow time off for court ordered child access.