Leaving a job that reimbursed tuition.

Does anyone have any experience leaving a job that has paid tuition reimbursement? The employee handbook states that if the employee leaves before two years it must be paid back. Unfortunately, I have been miserable for the past year and I am ready to leave. I'm in the process of switching jobs, but I am unsure how my current employer will try to get their money back. Do they bill me the entire amount all at once?

Thanks for any help.