I had opened an issue (#1681) to discuss it but testing it ONLY with TerraFirmaCraft again showed this information:

[Server thread/INFO] [tfc]: World time and Calendar Time are out of sync! Trying to fix...
[Server thread/INFO] [tfc]: Calendar Time = 966858 (858), Player Time = 844, World Time = 860, doDaylightCycle = true, ArePlayersLoggedOn = true
[Server thread/INFO] [tfc]: Calendar is behind by 2 ticks, jumping calendar time to catch up

Comments:
• I had previously tested with TLauncher now I switched to ShiginimaLauncher but again I had the same problem.
• I downloaded everything again from Assets, Libraries and Forge, the entire .minecraft folder.
• Always generating a new world with each new test.

JVM arguments: -Xmx5G
JRE version: 1.8.0_261
Minecraft version: 1.12.2
Forge version: 14.23.5.2854
TerraFirmaCraft version: 1.12.2-1.7.11.169

Log file: latest.log

Duplicate of #1681 then.

In case it wasn't clear in my last comment, you are opening an issue about nothing. That log message is not the cause of an issue and is entirely expected.