In most cases it will be better if you take at least one resting day in Tanzania before you start climbing. This way you can rest from the long trip, gain some energy and acclimatize to the temperature and culture. Most international flights arrive between 20.00 & 23.00 hrs (8-11PM), and before you have your luggage, ass through customs and have driven to Moshi, it will usually be close to midnight before you can enter your hotel room. So if you start the next morning (at around 0800-0900), you will still be tired.

What's even more important, if you fly in from a different timezone your body needs to adjust before it can function effectively again. If you climb and eat during the times that your internal system is used to rest, you might feel bad on the mountain and get tired quickly and feel sick. This can last several days.

That's why it is better to start the climb one or more days later. You will enjoy it more and have a much larger summit success. Try to get into the local rhythm of eating and sleeping the moment when you land (or even better: on the plane).

This is also why several climbers from the USA, East Asia and Australia etc often choose to go on safari first: for safari, the jetlag does not matter much and you can use those days to acclimatise to the time zone and temperature (and even a bit to the altitude!).