Differences during Search in table view

We are working with a Contact table with 7.5 million records and are finding when we enter a name - eg. ‘John’ in the Contact search field (not global search) - and hit ‘enter’ – it takes almost twice as long to get the results as it does if we just type ‘John’ and DON’T hit enter.

If you hit 'ENTER" - is it a database call? – or is it still the FTS call? – something else is making it take longer — there is no way for the user to know that clicking enter takes longer.

If you don’t hit enter - and with a regular user that has ACL applied — if i type ‘John’ my results take about 7 seconds — if I do hit enter (which is a common expectation for users - eg. search in google - you need to hit enter) – it takes about 12 seconds ---- so definitely something happening that is different between hitting enter or just typing and letting FTS perform the search.

Any input on this front would be very helpful.