The Hunt is garbage and needs to be fixed

[Xhadial]

How long does an A rank usually survive in a train?

One hit is all you really need in order to get achievement credit. If you're doing it for the currency then that's when you really want to be in a party, as it's based on total enmity accrued.
- If you're a Tank, make sure you have your [Tank Stance] on, hit once or use a party buff.
- If you're a DPS, hit once or use a party buff - for Ranged you can even use Peloton.
- If you're a Healer, use a party heal, or just hit once or use a party buff.

I'll often use healer myself and I get full credit and rewards just using [Eukrasian Prognosis] or [Kerachole] as Sage or [Medica III] of [Asylum] as White Mage.