Here's an article on LegalZoom that outlines the minimum time necessary (they say 9 months). Creditors, for example, get 6 months in which to make their claims against the estate and the executor has 3 months to make a decision to dispute a claim. Disputing a claim will extend the time necessary to process the creditor's claims.
An estate subject to federal estate taxes (valued over $5.45 million) can take much longer - up to a year after the April following the year of death (based on when an estate tax return is due and how long the IRS is taking to issue a final letter).
From this NoLo article you can see that NJ estate tax returns are due 9-10 months after death and then one has to wait for the state to issue its tax waivers.
Here's another article that describes the typical time it takes to process an estate (average of 1 to 2 years) along with the types of issues that can extend the time. It also lists the process beneficiaries can follow in order to get the current status and perhaps nudge things along.
The executor is required to provide an accounting of the estate to the beneficiaries and will have to provide a final accounting to the probate court before final distribution. Either all beneficiaries will have to agree to the accounting or the court will have to process the accounting and approve it.