Do lanyards have a service life? If so, what is that time-frame?

From an OSHA perspective, there is not a shelf life for fall protection equipment (nor any other PPE). Manufacturers may impose a shelf life and you may want to respect that. What OSHA does expect is a thorough inspection before each use. In 1910.132(e)—General requirements for PPE, it says: Defective or damaged personal protective equipment shall not be used. In 1910.140(c)(18), it says: Personal fall protection systems must be inspected before initial use during each workshift for mildew, wear, damage and other deterioration, and defective components must be removed from service.

1910.140(c)(4)-(c)(6) address lanyards:

• (c)(4)—Lanyards and vertical lifelines must have a minimum breaking strength of 5,000 pounds (22.2 kN).
• (c)(5)—Self-retracting lifelines and lanyards that automatically limit free fall distance to 2 feet (0.61 m) or less must have components capable of sustaining a minimum tensile load of 3,000 pounds (13.3 kN) applied to the device with the lifeline or lanyard in the fully extended position.
• (c)(6)—A competent person or qualified person must inspect each knot in a lanyard or vertical lifeline to ensure that it meets the requirements of paragraphs (c)(4) and (5) of this section before any employee uses the lanyard or lifeline.

For construction work, the OSHA requirements are at 1926.502(d) and say:

• (d)(19)—Personal fall arrest systems and components subjected to impact loading shall be immediately removed from service and shall not be used again for employee protection until inspected and determined by a competent person to be undamaged and suitable for reuse.
• (d)(21)—Personal fall arrest systems shall be inspected prior to each use for wear, damage and other deterioration, and defective components shall be removed from service.