Winners don't check won keys

Many users who are always online are just bots, this is why they never reveal the keys: no actual human opened the page yet to claim them. Usually they take their wins around weekends.

If they do not reveal the key for a week, screenshot it and ask for a reroll due to not being able to contact winner.
If they reveal the key and do not say anything, send a request received feedback with the same screenshots. It takes a few weeks to process, so be patient.

You can create a ticket named "Request Received Feedback" from support.
Im late 10 seconds

Can you open ticket for new winner?

Directly from FAQ.

The winner has not redeemed my gift, and I'm unable to get into contact with them. How do I proceed?

If you've been unable to reach the winner of your giveaway using e-mail and Steam after seven days of your giveaway ending, and they have not yet activated or redeemed any keys or gifts you attempted to send, please contact support to request a new winner. When creating a ticket, we ask you to include data that suggests you made an adequate attempt to contact the winner, such as screenshots of e-mails, friend requests, or gifts pending on Steam. If the request is approved, a new winner will be generated by the site.

The winners have 7 days to activate the won games, regardless if they are online in the meanwhile or not. It's just common courtesy to activate as soon as they can, but not a rule.
You have to wait until the 7 days to pass to reroll for a new winner (if they don't check the keys) or for request received feedback if they did.