There is no reason why you cannot apply for a conditional order on the due date. That in itself doesn't affect anything and it is what confers jurisdiction on the court to make a final order relating to the finances - whether agreed or whether an application needs to be made because you are not agreed. What you should not do - without first taking advice - is apply for decree absolute before the finances are settled.
I am not an enthusiast of exchanging Forms E on a voluntary basis. Mediators don't require the completion of Forms E and if the other spouse will not enter into mediation then there is no good reason why agreement should be reached after the voluntary exchange of Forms E. Typically the voluntary exchange of Forms E just runs up costs and wastes time. If the other spouse will not try mediation then it is usually better to make a formal application to the court to settle the financial issues. Then at least there is a determinate time table for the exchange of Forms E, the submission and answering of questionnaires etc. And, of course, even though a formal court application has been issued there is nothing to preclude trying to reach agreement at any stage (and the court encourages people to do so). Form E is designed for this formal process rather than being intended for voluntary exchange. You are already finding out what the disadvantage is not to not having a determinate time table.
Of course, you may, for one reason or another, have good reason to spin things out. There can be many rational reasons for doing that. However, if you look at things objectively and discover that in fact it is your spouse rather than you who gets the main benefit from delay then the sooner you issue a formal application the better.