Does Army ERB put promotions early?

if you mean listing it on an ERB before it has been announced and placed on orders, NO. Not with intent and by regulation and policy.
I would defer to an S1 SIDPERS clerk or supervisor for an "official" answer, BUT pretty sure a rank change on the ERB is a SIDPERS action, and pretty sure no SIDPERS clerk is going to process that action with orders for promotion.

Now that said.. could an SPC make point cut off, orders are produced and processed by S1 before they make it to a company for announcement and promotion ceremony?
You bet, more in the NG or reserves where you are not at the company every day

No. Promotions are entered and dated on the ERB for the day they are effective.