As you can see on the calendar, there is an overlap of two Firefox versions (52.0 and 52.1) to allow administrators to check for issues and prepare for updating. There can always be unexpected delay if there are problems, but normally you can expect that the dates posted are are correct.

See also Releases Scheduling on the Calendar web page.

Normally there has been eight major updates for a ESR version. Since there was a Firefox 50.1.0 there was a Firefox 45.6.0esr which would have came out in line with the 51.0 Release instead. This mean 45.9.0esr will be the last unless Mozilla extends support.

The image is a bit incorrect since it says 45.6.0esr was out at time of 50.0.1 Release when it was 45.5.1esr.

Thanks James and cor-el. Good to know that the final 45 esr will be as late as 4/18. Trying to squeeze out every last drop of the 45, since I know that I will have to redo my Profile, currently somewhat glitchy but still serviceable, before I can upgrade to the 52 esr. Know it's going to be huge job, so want to put that off as long as possible.