寅 holds three to five in the morning and, in the year, 立春 — the true start of the year in the Chinese calendar. BaZi doesn't change year at midnight on the first of January; it changes at 立春, which is to say at 寅. That tells you how load-bearing this branch is: it's the starting line of every cycle.
寅 is yang wood, imagined as a forest tree. Its character comes from that: ignition, outwardness, growing upward. It isn't good at maintaining and isn't good at detail. What it's good at is turning a thing that doesn't exist into one that does.
Where 寅 sits in a chart, that area arrives early, moves fast, and needs someone to take the baton. The tradition counts 寅 among the 驛馬, the travelling horses, tied to movement and changes of place — not restlessness, but a function that points outward.
