So if we do speak about online lotteries or casinos then the best approach or thing to be done if there's no mentioning about prize expiration then
it would be wise that you should really be asking on the support or team directly so that everything would really be clarified out.
I've never played lottery on online casinos or bought lottery tickets online, tbh. But I assume if you get lucky and you win, the prize will be credit to your online account automatically without having to claim it. Am I right? If yes, then there is no need to worry about expiration dates in first place! However, you should be aware that some casinos have the right to close your account and freeze your money if you remain inactive for a long period. So better check this on the casino's terms of service.