Seven days is tight, I’d have been irritated too. Since then I note the expiry date on my phone the moment I activate anything, and that habit has saved me twice. On a UK forum thread about bonus terms,
MegaFishWins UK Casino was mentioned by a few British players as stating the validity period right beside the offer, and one of them said so after finishing three bonuses back to back. For me the window was around thirty days from activation, and the time remaining showed in my account, so no sums were needed. A no-deposit offer had a shorter window than the welcome bonus. Always check the date on the live page before you click activate, because terms vary between promotions