I was there at Nathia Gali Murree on 21st December...
Biking is not a good idea on the snowy and icy(sheesha road).
So avoid it...
Regarding snow position... It was snowfall in Murree and Nathia gali in the night between 20 and 21 December. In murree the road were clear.. No snow at all.. But ahead Khaira Gali upto Nathia Gali was dangerous due to sheesha baraf in evening on 21st December. The areas exposed to sunshine were clear of snow, all snow melted same day.
This was the first snowfall. After that still there is no snowfall there. Might be tonight or tomorow get more snow.
In my opinion biking idea may be dropped.
In snow you can bike upto Murree.. But nathia gali and thandiani will be a real challenge scary and dangerous.
In these areas usually snowfalls and melt in one or two days.
I was on murree on 13.02.2011, Not a single patch of snow... but nathia gali was full of snow.. and roads has more than one feet snow.
In the end, uptill now,, the roads are clear upto all your destinations and free of snow.. You may proceed on bike before the next snowfall.
Thanks