Hi John,
the free software AstroImageJ;
( http://www.astro.louisville.edu/software/astroimagej/ )
does have a facility within it’s DP converter page that provides BJD time either on board or tick a box and it supplies the time from the uni of Ohio site mentioned on other earlier reply. Some useful instructions and manual provided by Denis Conti at;
However, the accuracy is to 5 dp and 6 respectively and you will have to set the DP converter to your site and target’s RA and DEC and be sure to always update the leap second tab before use.
Regards, Eric