Taking a machine that uses a needle to lay the ink deep into the skin makes a tattoo, so this means a lot of tiny puncture wounds are being made. There will be some bleeding. Under normal circumstances this will not be great. The main thing to avoid is drinking alcohol. Alcohol has a thinning effect on the blood and will produce a much greater amount of blood loss. No reputable tattooist will perform their services on one they know to have been drinking.
Depending on the size of your design and how long your tattooist is willing to work at any given moment will dictate how long it will take to get a tattoo finished. If it is small it can be done in one sitting usually in about 30 minutes to an hour. Medium to large sized tattoos can be done in one session. However, sometimes they are done over a period of several sessions some days apart. Very complex and large tattoos are almost always done over several sessions.