> elisp:
 > -------
 > (setq foo-font-lock-keywords
 >       '(("\\(\\(?:Fri\\|Mon\\|S\\(?:atur\\|un\\)\\|\\(?:T\\(?:hur\\|ue\\)\\|Wedne\\)s\\)day\\), \\(A\\(?:pril\\|ugust\\)\\|December\\|February\\|J\\(?:anuary\\|u\\(?:ly\\|ne\\)\\)\\|Ma\\(?:rch\\|y\\)\\|\\(?:Novem\\|Octo\\|Septem\\)ber\\) 
[0-9]+, -?[0-9]+\n=+$" . font-lock-keyword-face)))
 >
 > (define-derived-mode foo-mode fundamental-mode
 >   "foo"
 >   (set (make-local-variable 'font-lock-defaults)
 >        '(foo-font-lock-keywords t))
 >   (set (make-local-variable 'font-lock-multiline) t))
 >
 >
 > sample input file:
 > -------
 > Friday, May 5, 2006
 > ===================
 > 9.00 Xxxx Xxxxxx Xxxxx xXxxxxxxxxxxxx
 > 15.20-15.50 Xxxx Xxxxxxxxxxxxxxxxx
 > 17.30-19.00 Xxxx Xxxxxxxxxx
 > 18.00-19.30 Xxxx XXX
 >
 > Monday, May 8, 2006
 > ===================
 > 8.00 Xxxxxxxx xx Xxxxxxxx Xxxxxxxxxx xxx Xxxxxxxxxxxxx
 > 14.30 Xxxxxx XxxxxXXxXxxxxx xxx Xxxx
 > 15.30-17.00 Xxxx XxxxxXX
 > 16.45 Xxxx xxx XxxxxXX xxxxxxx
 > 17.15-18.15 Xxxx XxxxxXx
 >
 > Tuesday, May 9, 2006
 > ====================
 > 14.50 Xxxx xxx Xxxxxxxxxxxxxxxxxxxxx xxxxxxx
 > 15.30-16.00 Xxxx
 >
 > Wednesday, May 10, 2006

<----------------------------------- end of font-lock-fontify-region

 > =======================
 > 20.00-21.15 Xxxxxx Xxxxxx

`foo-font-lock-keywords' will fail to find a match when the end of
`font-lock-fontify-region' is positioned as indicated above.

Earlier it was possible to handle this - in most cases - by setting
`font-lock-lines-before' to 1, but I don't know how this will be done in
the future.  So far you could try the largely untested code I attached.

As soon as `font-lock-extend-region' has undergone its final revision
you should be able to replace the after-change-hook by writing an
appropriate `font-lock-extend-region-function'.  If
`font-lock-extend-region' will be regularly called by say
`font-lock-default-fontify-region', you will have to simply check
whether the first character to be fontified is an "=" and you may use
your original code practically unchanged.