CSMT-Tilak nagar - 30 mins
Tilak nagar - ltt - 5-10 mins.
Now you are left with almost 70 mins. In 70 mins, grant road to CST and then to Tilak nagar will be dificult at 7 pm. Even if you make it in around 40 -50 mins, still you can't be sure that you will be able to catch 1st local after you arrive CSMT. So, according to me its quite difficult. If other option available, please go for that