Hello! Thanks for asking about the Kosher lifestyle. The short answer is, while the Jewish law book, the Halakha, dictates that Jews avoid eating certain "non-kosher animals" like shellfish and pork, meat and milk together and "improperly" slaughtered meat as well as avoiding all forms of labor during the Shabbat, there are variances to the Kosher lifestyle which is based largely on two laws: the Kashrut dietary laws and Shabbat laws. While some Jews adhere strictly to the rules, others are selective.
Below is a deep dive for the Kosher lifestyle: what it means and the variances in the way it is practiced among Jews.
Following the Kosher lifestyle is essentially living by the rules of the Jewish Halakha, which is a book of religious laws. Two important laws are the Kashrut dietary laws and Shabbat laws. According to the Jewish law, in order to be said to practice the Kosher lifestyle, 3 general rules or commandments must be kept.
1. Avoid eating non-kosher animals (fish that don't have fins or scales e.g. shellfish, cleft-hooved animals that don't chew their cud e.g. pigs, and birds like vultures, hawks and ostriches).
2. Avoid eating meat and dairy together.
3. Do not eat meat that wasn't slaughtered according to the "Shechitah", the guidelines for slaughtering animals.
However, Kosher is considered a personal practice and there are variations in the degree to which Jewish people observe the Kosher lifestyle.
The Strict Observers
The more observant Jews adhere strictly to the Shabbat laws and eats only Kosher foods. "Shabbat is observed starting minutes before sunset on a Friday evening until the appearance of at least three stars in the sky on Saturday night." During Shabbat, Jews are expected to avoid all functions that are regarded as labour such as cooking, driving and writing. It is essentially a period of rest.
Observant Jews in accordance with the Kashrut laws do not eat meat and milk together or eat meals that don't contain either milk or meat. In order to ensure that meat and milk are not eaten together, a generally accepted wait time of 6 hours is observed between meat and milk, although it may vary. Some traditions observe this wait time "because of the nature of meat": it leaves fatty residue in the throat and might be stuck between the teeth and time is required for saliva to break these particles down. Orthodox Jews don't consider the wait time as just tradition but because it is Jewish law. Wait time between milk and meat, however, is minimal. It essentially requires that the milk taste is erased from your mouth, mouth rinsed and hands washed.
The less strictly adhering Jews choose to follow the rules mainly during "high Jewish holidays" such as the Passover, at which time the rules are even stricter. The Halakha prohibits eating foods made from grains and water that are allowed to rise. These foods are known as Chametz. They are prohibited because after the Jews escaped from Egypt, led by Moses, they didn't have time to allow their "bread rise before going into the desert".
The Halakha is the basis for the Kosher lifestyle which (based largely on two laws: the Kashrut dietary laws and Shabbat laws) requires that Jews do not eat non-kosher meat, do not eat meat and milk together, only eat meat slaughtered according to Shechitah and avoid all forms of labour during the Shabbat. There are however, variations in the extent to which the laws are kept in the practice of Kosher.