How long does can a Jehovah's Witness not practice their faith before they are separated from their church or Kingdom Hall?

Answer 1

Every situation is different.

A person is considered a Jehovah's Witness when they are baptised. If an unbaptised person wants to separate themselves from the congregation, they simply stop coming to meetings. Of course, members of the congregation will, along with who ever has been conducting Bible studies with them, would be very concerned, and would visit them to see about their well-being. Sometimes a person gets discouraged, or there may be some hardship they are experiencing that the congregation can help them with. But as far as the organization's worldwide congregation records, officially that person was never fully integrated into the congregation. If later they want to start back again, they are welcome to begin attending meetings and studying The Bible again.
If a person who is baptised as a Jehovah's Witness wants to remove themselves, they submit a letter of intent to remove themselves from the congregation to the local congregation elders. The elders will meet with the person to make sure that this is what they want to do. The elders then inform the worldwide headquarters so that the records can be updated there, and the congregation is informed that this person is no longer a "brother or sister."

If the person is guilty of gross misconduct such as criminal behaviour, or something that the Bible condemns such as sexual immorality, and if the elders meet with this person to try to counsel them from the Bible to stop their sinful course, and if that person refuses to quit committing the offenses and show an unrepentant attitude, then the elders will remove that person by "disfellowshipping."
In either of these two cases, if later the person has a change of heart, and wants back into the congregation, they can submit a letter to the elders that they want to be reinstated to the congregation, and the elders will discuss with them the steps that they can take to rejoin the congregation.

Sometimes a Jehovah's Witness who is baptised doesn't actually leave the congregation under any of the above circumstances, but they simply become "inactive." They may stop coming to meetings and/or stop engaging in the public ministry. The congregation will be very concerned and the elders and congregation members will be very active in encouraging that person, and offering whatever assistance that they may need.
In all of these cases, there is no set time for this to occur.

It can come very quickly, or may happen gradually.

But if a baptised Jehovah's Witness doesn't actually get formally separated by a self-instigated action like a letter, or by the elders performing a "disfellowshipping" action, then that person is still considered a "brother or sister," even though they may be "inactive."

Answer 2

It ultimately depends on the individual circumstances and decisions of the Jehovah's Witness congregation or elders. Generally, if someone consistently fails to adhere to the teachings and practices of their faith or publicly denounces it, they may face expulsion or disfellowshipping.