when using temporal breach on thousand tail watcher. does it play it free including acceleration cost?

No — Temporal Breach makes Thousand-Tailed Watcher free, but not the Accelerate cost.

Temporal Breach lets you play the unit "ignoring its cost," which zeroes out only its base costs (7 energy + 1 Mind power, per Rule 356.1.b.1). Accelerate is an optional additional cost, not a base cost, so it is not ignored (Rule 356.1.b.3 — the Legion Rearguard example is exactly this). You may choose to pay Accelerate's 1 energy + 1 Mind power so the Watcher enters ready, or decline and it enters exhausted — either way the "When you play me" trigger fires normally.