[FIX] VALORANT stuck offline with greyed-out Play button? Check your Windows clock!

I spent around 7 hours trying to get VALORANT working, and the fix turned out to be something incredibly simple: my Windows date and time were incorrect.
I’m posting this in case someone else runs into the same issue and wastes hours troubleshooting it.
The problem
After installing VALORANT, I opened the Riot Client, but the VALORANT page appeared to be offline. The Play button was greyed out, and trying to repair the installation didn’t resolve anything.
I initially suspected an issue with Riot Vanguard, Windows services, or my ReviOS installation.
What I tried
I spent hours troubleshooting and checking various things, including:
Checking Windows services such as Base Filtering Engine (BFE), Windows Defender Firewall, Windows Management Instrumentation (WMI), and DNS Client.
Checking whether the Riot Vanguard service (vgc) existed.
Checking whether Riot Vanguard was installed in C:\Program Files\Riot Vanguard.
Looking for potentially problematic Windows registry settings, including DevOverrideEnable.
Checking the Riot Client logs to identify the actual error.
None of these checks revealed the underlying problem.
The actual cause
When I finally inspected the Riot Client logs, I found these errors:

Dependency DirectX failed to install
SSL certificate problem: certificate is not yet valid

The logs also contained SSL certificate validation errors when the client attempted to access Riot’s CDN.
This was the key clue. The certificate error indicated that Windows was evaluating a certificate as not yet valid. My Windows date and time were incorrect.
SSL/TLS certificates have validity periods. If your system clock is incorrect, certificate validation can fail, preventing applications from establishing secure connections to their servers.
The fix
I corrected my Windows date and time. That’s it.
After fixing the system clock, the certificate validation issue was resolved, and VALORANT was working again.
If you’re experiencing the same issue, try this first
Before reinstalling VALORANT, reinstalling Vanguard, changing registry settings, or modifying Windows services, try the following:
Open Settings → Time & language → Date & time.
Enable Set time automatically.
Enable Set time zone automatically, or select the correct time zone manually.
Click Sync now under Additional settings, if available.
Restart the Riot Client and try launching VALORANT again.
If the issue persists, check the Riot Client logs for SSL errors, particularly messages such as:

SSL certificate problem: certificate is not yet valid

This error can point to an incorrect system clock, although other certificate-validation problems are also possible.

I spent seven hours investigating Vanguard, Windows services, registry settings, and the Riot Client, only to discover that my system clock was wrong.
If Riot Client appears offline, the Play button is greyed out, and the logs show SSL certificate validity errors, check your Windows date and time before attempting more complicated fixes.
Hopefully, this saves someone else a few hours!