Check if system time is set correctly with respect to your current time zone.
If you use Kaspersky Antivirus - you need to add War Thunder to the trusted applications:
1. Open Kaspersky Antivirus.
2. In the lower-left part of the window, click the link Settings.
3. In the **Settings** window, go to the Additional section and select Threats and Exclusions.
4. In the Threats and Exclusions settings window, click the Specify trusted applications link.
5. Click Add button in the lower-right corner of the opened window.
6. Navigate to the game folder and select aces.exe.
7. Check every box in the opened Exclusions for application window and press Add button.
8. Repeat steps 5-7 for launcher.exe
Also go to Network Settings and make sure that Scan encripted connections checkbox is not marked.