दौड़ती है हिमालय तट से सागर, हमसफ़र हर राह पर, हवाई जहाज़ों को त्याग कर, करो अक्सर, भारतीय रेल में सफर. - Arpit P

If
1. you are coming from CR side,
2. your train terminates at CSTM,
3. you have to go to BDTS to catch another train,
4. you have heavy laggauge
5....
more...

its not evening time i.e 4.30p.m to 9 p.m,
and 6. you are alone,
then, don't deboard at dadar. Instead go to CSTM and then catch the CSTM-Bandra-andheri Harbour local. As these local start from CSTM,you have 70-80% probability that you will get seat or else a place to stand.
Alight it at bandra and then go to bandra east side. There you will get sharing auto or even personal auto to BDTS. From bandra to bdts,it will hardly take 10 min.
Also if you have less laggauge,and you want to reach quicker,then take slow WR local from dadar towards virar side and alight at khar road. Its just 5 min walking distance from khar road to bdts.