1 year (8760 hours).
No. The maximum is 1 year. This is enforced by Tailscale. tailscale key expiry
# Generate a key expiring in 72 hours tailscale auth-key --valid-for 72h tailscale auth-key --reusable --valid-for 2160h Generate a key expiring in 1 year (max) tailscale auth-key --reusable --valid-for 8760h 1 year (8760 hours)