It's happened to me many time before but now I think I have a consistent way to trigger this.
1. Spectate a game until its completion
2. After the victory screen go to your profile and first win will be shown as available.
3. Relog and the issue will be fixed.
This happened twice today. Also I tried spectating and immediately leaving (before the game completed) and the timer was still normal.
League of Legends Community
ShadyElf ?? Senior Member