Battery Life

The product :
LiPo Battery Pack

If this is powering my RPI3 and I am using the camera how long can i expect it to last please?

It depends on how much current is being drawn and how big the battery is. The higher the MAH rating of the battery is the longer it will last before it gets discharged.
You don’t say which battery you plan on using and what upconverter you want to use it with. LIPO battery voltage has to be boosted to 5V to power a Raspberry Pi.
A 3b draws ~400mA at idle.