Ok - that is better.
If there was no direct wording, then you would have needed to serve a S.21 notice and wait 2 months, or wait until the tenant was in breach of the agreement and serve a S.8 notice.
You would have risked being sued for an unlawful eviction, which is why I needed to be quite sure about what was said and any discussions.
That is why I needed to be absolutely clear about what was said, agreed and discussed.
On the basis of this I can answer your questions in order:
1. Yes, the parties can agree whatever terms they want.
2. As soon as you take back possession
3. You can enter once the agreement has been fulfilled.
On the basis the deposit was released, payment of £450 was agreed and Council tax etc done, then you can take back possession now.
Clearly, a new tenant would be liable for Council tax from the time they moved in. But on the basis of the agreement and actions taken, then you can take back possession and re-let.
Can I clarify anything for you about this today please?
If not I would appreciate a positive rating for my answer. If you need more help, you can ask follow up questions for free and I would be delighted to assist. Thanks!