You may consider taking route 963 to Woodlands. Make a transfer to route 168 there, and then alight when you reach the old Jalan Kayu bus terminal (outside the old Seletar Camp gates). I don't know which point along Edgware Road are you going to, but if it is nearer to the Seletar Airport area, grab a taxi if you are
really pressed for time. Otherwise, unless you are very lucky, you will have to wait more than 20 minutes for the route 103W bus (get off before it reaches the second roundabout on it's way in - ask the bus captain if you are not sure). If it's nearer to the old camp gates, I suggest that you walk in.
The time taken should be around 1 hour plus - route 963 takes about 30 to 40 minutes to reach Woodlands from Hillview, and about another 30 minutes for route 168 to get to it's Jalan Kayu detour, judging by my estimates. It may be faster though - my boldest estimate (and if you are lucky enough to have near-instant transfers and drivers who speed on expressways (

)) is 40 to 50 minutes.