A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Richard B. Langley
Date: 2021 Jan 6, 06:25 -0800
"By international agreement, any difference is supposed to be nulled out by leap seconds if it is predicted to grow greater than 0.8 seconds (at least if I remember correctly, that's the limit)."
0.9 seconds is the limit:
"The IERS is responsible for the announcement of leap second insertions, following a procedure described in a recommendation adopted by the Radiocommunication Sector of the International Telecommunication Union (ITU-R). By this process, the value of UT1-UTC is kept below 0.9 s." (from BIPM website)
-- Richard Langlwy