Right now, people have to guess from the document the format of the timestamp after the date.

The timestamp can be any of the builtin formats that lnav has, see https://github.com/tstack/lnav/blob/master/src/time_formats.am for the full list. You can also press TAB and one of the first suggestions is the timestamp of the top line in the view.

Also, it seems unintuitive to have to specify till seconds in order for it to work such that :goto 2017-01-01T20:00 (not specifying seconds) will not navigate to 20:00pm but to the first line in the day 2017-01-01.

It looks like the format without seconds was missing, I've added it in c24be23. I've also added a check to make sure the full timestamp is consumed. If it isn't, an error like the following should be shown:

Thanks for the report!