A practice putt after holing out is fine, providing you don't hold up the group behind you.
Rule 7-2 states:
A player must not make a practice stroke during play of a hole.
Between the play of two holes a player must not make a practice stroke, except that he may practise putting or chipping on or near:
(a) the putting green of the hole last played,
(b) any practice putting green, or
(c) the teeing ground of the next hole to be played in the round,
provided a practice stroke is not made from a hazard and does not unduly delay play (Rule 6-7).