How long can it take for pneumonia to spread from just one lobe of one lung to all of both lungs and get into the blood stream?

Very fast: That can happen very fast. Bacteria double every 20 minutes. 2 4 8 16 32 64 128 256 512 1024 2048 4096 8192 16384 and so on one million in 7 hours.

Depends: If you are very young or elderly it can be very serious. If you have a strong immune system you may fight it longer. A lot depends on what organism is causing the pneumonia. Some are more aggressive than others. For some it may be a matter of hours and some it may be days.