The bulk, if not all the fees charged by the agent in respect of the transfer itself will almost certainly be paid on day one. Yes by the very way it works some of the players wages and as a consequence the agents% can be spread but that doesn't alter the fact that Everton will have had to pay way over 20% of whatever fee has been agreed
You can relate agents fees to 'sweat equity'; this is why they can be deferred. The fees are only liable after the work is completed.
That means any associated taxes are also only due after the work is completed. After when payments were due.
This is probably the cause of the delay and a few complications, negotiating the contracts for payment.
Despite what Andy Hunter has said to probably try and embarrass Everton - I am not concerned.
Negotiating a contract - about WHEN the fees are due is no issue.
BTW 'sweat equity' would be a criteria in trying to determine if the fee is a legitimate fee or not (e.g. a bribe). Also the nature of the work would be covered in the contracts between the club and the agent/player as needed.