I haven't ever had a date that was followed by a period and a decimal digit that wasn't a timestamp, but if you do encounter (or can reasonably predict) that ambiguity, I defer to a standard format.

I find the . significantly easier that T to deal with when I'm looking across timestamped backups of config files or whatever. The T really throws me off as a "separator" character, it makes both the day and hour harder for me to read.