I would personally drop the apostrophe as this is suggesting 'of one year'. The sentence really means 5 years (of) practical experience, 'of' being understood. QM1 is gramatically correct but years' is not offered as an option and I think the tradition in recruitment is to disregard the possessive factor in terms of the apostrophe.
There's no fight involved, Annie! The sentence actually means "the experience of five years"...ie the experience belongs to the years in effect... which is without a doubt plural. When changed to the "five years' experience" format, clearly the apostrophe must come after the final 's'.