Of course it's possible but you have to be very good at priorities and be consistent.
From the start the creator of this clone site already had 50 plus blogspot and wordpress self-hosted sites. The plan was to try as many niche as possible and see which one brought in the money. The trial is still on-going and usually effort is placed into the blogs that bring in the moolah. Currently there are 10 active blogs that are being maintained.
Of course our cloned blogs are all different in some way or another especially in content. Some are related but we have tried our best to separate them and give them each unique flavours.
How to dedicate time to each blog
We keep an excel spreadsheet to see the frequency of updates for each blog.
We also keep track of our ad revenue such as Google Adsense to see which channel is performing well. Sometimes we will just update an old site because it's been forgotten. Adsense channel is particularly useful here as sometimes high value clicks come from forgotten blogs. Our experience is that forgotten blogs with low page impressions can suddenly 50cents to 1 dollar per click - most probably because of smart pricing.