Can the pre-employment medical be done in-house?

Initial, periodic and follow-up exams are performed by an occupational-health provider with which the employer has a contract — this cannot be done "in-house". The employer bears the cost; the exam is, where possible, during working hours.

Without a valid certificate you must not allow work — neither on day 1 nor after the previous certificate expires. After an illness longer than 30 days — a mandatory follow-up exam before returning.