Yes - total journey time give or take a few minutes. You are able to check in for many flights from Shenzhen airport at the Cross border Bus Terminal at Kowloon Station, so arriving one hour before the flight departure time at Shenzhen Airport is usually ok.
Here is the bus schedule. They actually quote 75 minutes journey time, but in my experience it is closer to 100 mins.
It's quicker and easier to use HKIA, but you are saving money using Shenzhen airport.