If you haven't already done so, check their website or email the DGS about this. Some schools do not like to accept their own MA students (i.e. Oregon) while others have a track record of taking their own (i.e. BC). Plus, if they accepted you to their MA they must have some interest in you, and you expressing interest in continuing forward in their Ph.D program will perhaps open that door a smidge.
I think they are asking to let them know what we think in 3 weeks, but they said that we can take more time if we need it. At least that's what my email said.
Some schools accept more than their grants for funding allow so as people decline they later offer more money. Or there's been word that some schools don't even have their funding lined up yet so they might have accepted you but are waiting to hear back from the school if there is more funding to be had.