First of all - you are overworrying the weight thing! It is weight loss over time that you need to be concerned with. You should be weighing at the same time each day, the amount of food, water and exercise they get in any given 24 hour period can affect their weight greatly. If a chin is very ill or is a newborn kit, you should be weighing everyday. If it is coming out of an illness and seems to be eating and drinking okay then you can weigh every couple of days or once a week - but always at the same time. Monitor water levels, food levels and poop in addition to weight and note any changes.
If I am monitoring a weight I weigh first thing in the morning right before I feed the chins, others do it at night, whatever works best for you. The critical thing is to be consistent. 10 gms is not that significant in an older chin. By constantly weighing the chin you could be stressing him out - relax!