Intimacy with husband during ramdhaan

slmz mufti saab.i got married in June 2008 and im staying with my mother-in-law in the same house.it is almost Ramadaan and i wanted to know if it is permissable to be intimate with my husband after magrib and when must i make ghusl? Must i make ghusl before sunrise? Or can i make niyah for fasting and ghusl in the day before 12pm?
the reason why im asking is because i dont want to make it obvious to may mother-in-law that i was intimate with my husband as i feel shy and uncomfortable.
my husband and i want to have a baby.please advise as to what niyah must be said before conceiving and what niyah must be said before having intercourse.

Jazakallah