The Titan submersible was estimated to have a 96-hour supply of breathable air when it launched Sunday morning in the North Atlantic. That means the deadline to find and rescue the sub is roughly between 6 a.m. EDT (1000 GMT) and 8 a.m. EDT (1200 GMT), based on information the U.S. Coast Guard and company behind the expedition have provided.

from Times of India https://timesofindia.indiatimes.com/world/rest-of-world/search-for-the-missing-titanic-submersible-nears-the-critical-96-hour-mark-for-oxygen-supply/articleshow/101189803.cms