I think the 750ms delay is only needed when you are running in parasite power mode, since you have to give the sensor time to "steal" power from the DQ line and charge up enough juice to perform the conversion.
From the Maxim Datasheet (http://datasheets.maxim-ic.com/en/ds/DS18B20.pdf):
CONVERT T [44h]
This command initiates a single temperature conversion. Following the conversion, the resulting thermal data is stored in the 2-byte temperature register in the scratchpad memory and the DS18B20 returns to its low-power idle state. If the device is being used in parasite power mode, within 10µs (max) after this command is issued the master must enable a strong pullup on the 1-Wire bus for the duration of the conversion (tCONV) as described in the Powering the DS18B20 section. If the DS18B20 is powered by an external supply, the master can issue read time slots after the Convert T command and the DS18B20 will respond by transmitting a 0 while the temperature conversion is in progress and a 1 when the conversion is done. In parasite power mode this notification technique cannot be used since the bus is pulled high by the strong pullup during the conversion.
In the code I use for reading DS18B20 sensors without parasite power I have either 100ms or zero delay between issuing the CONVERT T [44h] write to the scratchpad then reading the results of the conversion and both seem to work fine. Keep in mind I am cycling through the sensors found from a "search" request one at a time and reading each one individually. It seems the time it takes my Arduino to issue the reset to the 1-Wire bus then "select" the particular sensor it is working with so it can then read the temp from the scratchpad is enough time for the DS18B20 to finish computing the temperature.
If you like just keep lowering your delay to zero and stop when it doesn't work anymore - you can't really break it. In my experience 100ms should be more than enough time if you don't feel comfortable with zero delay.
FYI - In the code I use for reading temperature and voltage on the ADC of a DS2438 I do wait 100ms each for temp/voltage conversion, but I haven't had a need to try to shorten that yet.
Hope it helps,
willnue