Entrance is great spell, but I always though that it has a SILLY casting time (ONE FULL ROUND!).
On the other hand, waiting until you get the "Adept" feat (12th level, at least) is definitively too much.
So I try to fix this with a feat like this:
NEW FEAT:
Powerful Mesmerizer
Your skill in entrancing people is amazing.
Prerequisites: Magic Bab +3, Hypnotism Sorcery style, Cha 15 or more
Benefit: You do not need to spend "One full round" to cast "Entrance", but you can cast it as a standard action.
Furthermore you are able to entrance people of higher level.
The maximum HD you can entrance is equal to 6 or your scholar level (whichever is higher).
If you want to entrance higher HD victim you must spend one-full round (as per normal Entrance rules) for entrancing a victim of your scholar level+2.
Every other full round you wait you can add another +2 to the maximum HD.
Normal: Entrance needs one full round to work.
Special: If you like it, you can choose this feat in lieu of a New Sorcery Style.
If you have the "Adept" feat with Hypnotism you can cast "Entrance" as a move, standard or free action (your choice), allowing you to cast also another Hypnotism spell, which is an exception from normal "adept" rules.
For example, it allows you to cast a "Domination" on a subject you just entranced with your move action (entrance) in the same round.
With the "Adept" feat "Domination" is a free action, so if you have casted "Entrance" as a move action, you have still another standard action to use in the same round (but not for a third spell).