You don't usually need to separate time adjuncts with commas. (Therefore: 'I saw him at 10 o'clock', not 'I saw him, at 10 o'clock'.)
However, because of the comma after Friday, '3 July 2015' can be thought of as parenthetical, where generally a pair of commas is used; this means that the date is set off as parenthetical information.
I have been conditioned to expect two or none in this situation.
Cortege leaves on Friday, 3 July 2015, at 10.45am for cremation at Mandai Crematorium Hall 1 at 11.45am.
Cortege leaves on Friday 3 July 2015 at 10.45am for cremation at Mandai Crematorium Hall 1 at 11.45am.