I do 15-30 minutes on the bike (interval workout will have best results) but also I include other cardio such as the treadmill and rower. If you don't have access to a gym you could try outdoor low intensity jogging/power walking also.
Thigh fat is stubborn, I've had big problems trying to shift the inches from this area now I give up and on top of cardio and running outdoors I squat with weights. There is a lot of conflicting information and personal experience if squatting helped thin the thighs or not so waving my white flag a year later and if they're staying I would prefer them more lean lol, time is still to show the personal results for me
Also good for the legs:
Jumping jacks
Lunges
Skipping