Upon the successful completion of your transaction, you will receive an email confirmation.
Your email confirmation will state 2 dates:
The 1st date of the event and the date you have actually bought tickets for (further down in the itemisation)
You can also download your ticket(s) straight from your confirmation email, which will state the date that your ticket(s) will allow entry to.
If your ticket(s) are physical and posted out to your address, you can check the date through your confirmation email and through your order history.