Greetings of the day from Siddhivinayak Solutionss!!
The best day is 28th April 2018 for griha pravesh the pooja timings you can check with a Pandit.
And you are born in Dhanu Rashi (Purva Ashada Nakshatra)
As the flat you have bought is a South Opening Flat and as per your birth number it will affect the females living in that house.
So you need to take a guidance of an expert as the vastu could not be advised only on the entetrance and exit it is also seen that which place has slopes, extension, reductions and other factors and placements.