I get my carbs in early. It depends on what my day is going to be like. But say I get most of my carbs in the first 1/3 of my day. So its not only how many carbs but WHEN hes taking his carbs. Id say to stick around 200 but some people can advocate less. Personally any less than 200 and I feel like my muscles are shrinking. some may suggest this is glycogen depletion, but I dont like it. I feel like some of this is muscle. So like gorrillafit said his caloric needs should be assessed as well. With your dropped carbs your going to want to up his protein. Id suggest around 3-4 grams of protein per pound of weight. Also BCAA's become more valuable than ever during this time. Now 4-5 weeks is not gonna be easy. IMO its not enough time. Training would have to be definetly cardio, and lots of sprinting.

Its not just carbs, he needs to evaluate his base caloric needs, reduce those by about 500-1000 cals per day, with about 70-100gms of carbs\d all in by Lunch. The rest of the day its protein, veggies, small amounts of good fats for energy. Like a tablespoon of flax seed oil on his salads or veggies. He should be able to drop 1-2 lb or so of primarily fat. If he adds 1/2 hr carb depleted Morning Cardio maybe 1.5-2.5lbs\wk.

4-5 weeks is a small window, first thing that comes to mind when talking about dropping weight that fast is a keto diet