I don't think you should worry about getting "too muscular" at this stage to be honest. It will need to be a combination of healthy eating and exercise.
As suggested a full body workout 3 times a week would be a good way to start. When planning a full body routine make sure you are hitting all the neccessary muscle groups and that you are working them sufficiently to break them down.
If I was you I would go for a FBW: M, W, F and you can take the weekends as days off from weights but go and do cardio (About 20 minutes
HIIT is enough) on one of the weekend days. Have two days a week where you don't go to the gym though and you just rest.
After you weights each day do a 20 minute cardio session, start with just running on the treadmill. Try this (It might be too easy for you but give it a go I don't know how fit you are).
R - 3 Minutes (10.0km)
S - 1 Minute (13.0km)
So alternate between the two speeds for a total of 20 minutes. Use the interval training program on your gyms treadmill. Many would say not to do cardio on the same day as your weights but if you want to slim down first just tag the cardio on to the end of your Weights regime.
Lift weights 3 days a week. Do the cardio above 5 days a week. Making sure you have 1 days rest from the weights in between each FBW and ensuring you take two days off where you do not go to the gym.
You will not need 10 hours to do that each week.
If you are not used to going to the gym you could consider not bothering with cardio yet and just focusing on your weights until you get used to going to the gym regularly. This might stop you from getting sick of the gym too quickly. It is up to you though. I found when starting that not doing cardio and just doing weights made it harder when it came to adding in the cardio because I just wanted to do weights. I am used to cardio now though and it isn't that bad.