"Zero seven five seven" is the correct way to state the time, pronouncing each digit separately per the table below.
Aircraft call signs are sometimes grouped instead of annunciating each digit, for example United 6330 would be "sixty three thirty" instead of "six three three zero".
Otherwise, headings, time, coordinates, and all other numbers used in aviation radio communication are generally spoken individually, digit by digit.
It is important to note that in aviation the need for clarity overrides common English usage. For example, while it is common to pronounce the number zero as "oh" in the everyday world, aviators are taught that zero and O are distinctly different: One is a number, and the other is a letter of the alphabet. They should never be substituted for one another, or used in the wrong context.
Finally, the example you offered is incorrect because it isn't "seven hundred and fifty seven hours", past time zero, rather it is "seven hours and fifty seven minutes". (Except it isn't said like that...)