Scoring information is tied to Game Center, chances are high that you can retrieve your Mahjong times by signing back into Game Center to restore them. To sign into Game Center:
Access your device Settings (gray gear icon)
Scroll down to Game Center
Sign into Game Center with your Apple ID
Return to Mahjong and select the Game tab > Scores
Make sure you have a working, reliable internet connection to connect to and update Game Center leaderboards. For instructions and support on how to make sure you're logged-in to Game Center, please reference Apple's Game Center support page.