USCIS denied my I-765 for employment authorization. I submitted an additional evidence to reopen/reconsider the case. How long does it take for USCIS to issue me a new EAD card?
An I-290B Appeal or Motion to Reopen/Reconsider can take an extremely long time - anywhere from a few months to two years in my experience, but it depends where it was filed, whether the office of initial filing decides to handle it in-house as a Motion to Reconsider, what type of case, and many other factors.
You don't mention the basis for the EAD application - was this for Optional Practical Training, based on having an Adjustment of Status pending, something completely different? Why was it denied? IT may make more sense to simply refile it, addressing whatever issue was raised in the denial.
Consult an attorney for advise specific to your circumstances..