MIN have made an offer to you.The offer is unconditional.When...

MIN have made an offer to you.
The offer is unconditional.
When communication of the acceptance of the offer is received by the other party, even if they don't read it, is when the contract is accepted by both parties.
The date is when the communication is received - not processed which may takes days or weeks.
This means if you mail in your acceptance the date for calculating the consideration is when the registry receives your acceptance.
If you send it by email, it would be reasonable to assume that is the date.

If it is a conditional offer, then the date would be when the offer is closed or made unconditional.