How should I set my physical activity level?

Addis_Daddy12

I just started a new job a couple of days ago at UPS as a pre-loader. It is an extremely physically demanding position with being on your feet and moving boxes that weigh any where from 1lb to 70+lbs. This is for about 4-5 hours per day, 5 days per week. My question is this: under goals:activity level for MFP they have listed:L sedentary (which I have had listed since joining), lightly active, active, and very active and I am wondering to which one I should change my goals? The reason I am having trouble judging which one I am supposed to use, is because it specifically says "spend a good part of the day" i.e on your feet, doing some physical activity, or doing heavy physical activity. Well its really not most of the day and I dont know if it would be "a good part" since its only 4-5 hours. Just need a little help on judgement here. Because I dont want to set my calories too low, but I also dont want them to be so high that I actually slow my weight loss. Thanks for your responses in advance.