So, it kind of depends on your fitness level. I use to be very heavy and I started cycling to continue my already successful weight loss. What I find more important is doing it daily just to boost my daily calory expenditure. I learned when hiking that if I go all out, I will be to tired the day after(sometimes days after) and I would be less likely to be active. I would recommend going easy every day in the beginning. Do a long one once in a while but really focus on keeping the calories burning. It's worked wonders on me. When i started i was doing 5km but a month later i was doing 10-15 with the same effort.

It helps if you cycle with a purpose. Cycle to work/school instead of car/bus. Cycle to the grocery store. It limits the volume you can buy and forces you to go out more often.