It seems it's not only the timestamp server that's not working. I just discovered 'Trusted Site Seal from Comodo' (for EV SSL certificates) reports:
"This site is currently undergoing maintenance. We will be back shortly."
Although these are my first posts in this forum, I've been happily using Comodo certificates for over 10 years. But they are quite messing up now. The timestamp server is down for at least 17 hours...