If you have placed someone on salary and then you ask them to clock in and out or complete a timesheet with every hour worked could the company be liable for the overtime that shows up?

The government is pretty specific about who should and should not be classified as what they call exempt and non-exempt employees. When an individual is non-exempt they are entitled to overtime benefits.

You can get into hot water for treating exempt employees as non-exempt and for doing the reverse. For example, if someone is exempt, you can't dock their pay for leaving the office early or coming in late. If someone is non-exempt, you have to pay for their overtime and give them appropriate breaks.

You may require an exempt employee to track their time if there is a relevant business purpose to doing so. For example, lawyers are exempt (not entitled to overtime) but most are required to maintain detailed accounts of how they spend their time and submit them regularly. The purpose of this, however, is for figuring out how many hours to bill back to the client.

You should find out how this particular job is meant by the government to be classified. If they are non-exempt, they should report their time with a time clock or through some other method and must be compensated for their overtime, given proper breaks and so on. If they are exempt, do not make them punch a time clock (it's just not done) but if you need to keep track of their time for purposes of billing your customers, that's fine. A time clock wouldn't work for that purpose though - that would be a tough argument to make.

If you get caught not treating one person properly, you can be forced to pay huge fines and make restitution to all your current and former employees who were not compensated properly, so be careful.