Sorry for the delay in getting back to you. There is no time limit on redeeming a key.
If you go onto the download page for Loot Rascals, can you see a Steam key? You can get to the download page for Loot Rascals by going to this page (https://hollowponds.itch.io/lo...) when logged into your Itch.io account and clicking Download at the top of the page. You should see a Steam key at the top of the page just under the Itch download.
If not there might be a problem on Itch's side and I'll get in contact with them for you to get this sorted!