The image shows a divergence meter with the number 0.210327 on it, which can be read as March 17, 2021.
The tweet also includes the words:
"World line divergence number: 0.210317%
The story is 'reproduced'––."
世界線変動率"0.210317%"
— 科学ADV公式 #シュタゲ10周年 (@kagakuadv) March 11, 2021
物語は「再生産」されるーー。#シュタゲ pic.twitter.com/MMUKTq4m94