I think if your fitness levels are low, you have to break the sessions up...as you get fitter then you can go on for longer...I can do 2.5 hours at a stretch now if I need to...I need to build my stamina and endurance up even at this level of fitness so I can go for longer...
Little steps...before I could go our for a run without thinking about it, I used to run from lampost to lampost...run, walk, run walk...and in the gym I used to go for shorter spurts and then build them up, raise the weights in weight training...the better you get the more you can do...
Again little steps, even ten minutes here and there is fine, just up the intensity for those ten minutes...even walking gets you fitter...obvioulsy longer stretches as walking is low intensity...just walk faster for periods then slow down again, speed up again, etc...
I know many many people who mix and match workouts...I do weights and cardio and it works out fine for me...
Good luck!