A good question. It is something I’ve been looking at, but suspect such interactive maps are far beyond my technical expertise. I looked at producing the maps for different time frames (e.g. months) and time bands (e.g. hour of day). Here the problem is finding the time to do it and also a fear that Google maps is not terribly reliable so I’m not sure how consistently it would present the data to visitors. If you know of any useful mapping tools please let me know.
On the second point, can I say (hopefully) welcome to Wandsworth!