Fit4life - Wow! You have lost a lot of weight. Does it really matter if you have a slight gain or loss one week simply because you switched meeting times? I realize that it is very hard to not be obsessed about the numbers on the scale, but you need to try not worying about it so much. Following a healthy eating plan to lose weight is good for your health. Exercise is good for your health. Combine the two and you are a winner in the long run, no matter what the scale says one week. It will only affect your weigh in on the week you shift patterns. After that just be consistent before weigh in.
Most people are lighter after exercising because you sweat and do not drink enough water during exercise to replenish the lost water. This also affects the accuracy of body fat tests for the same reason. If you drink during and after exercise to replenish what you lost to sweat, you should weigh about the same.
It is not a good idea health wise to avoid water during or after exercise because of the scale. Any water lost during exercise is just a temporary loss and will ge regained as soon as you drink or eat anything.