Pension Contributions Time Limit

Pension Provider is claiming deadline will be missed unless their processing time (of 5 days) is taken into account. Is that right? Won't accept cheque or CHAPs post Wed for a contribution to be included as April 2012. Contribution is being paid by the company on behalf of the employee - not by employee himself which I admit would have to go through the payroll system but I still wouldn't understand the deadline being set if that were the case.

Thanks for any comments