Crankshaft position sensor location needed

It is underneath the rear of the engine in the bellhousing flange. It reads the notches on the plate next to the starter ring gear. Replacement is simple, go under the vehicle, remove the retaining bolt and the wire connector, install the replacement part and connect the harness connector. What is the vehicle doing that makes you think it needs replacement?

Okay, that still sounds more like a fuel issue. Try this test. Take a can of starting fluid or carb cleaner, with the engine cold in a way that it won't normally start, spray the starting fluid into the intake and see if it now starts. If it starts up "normally" it's a fuel issue. Could be a bad regulator or control module. If the starting fluid works I would then install a fuel pressure test gauge in the fuel line. Then try the same thing as above but just try to start it without the fluid and no key on time. If the fuel pressure doesn't jump to at least 50 PSI during cranking the issue is the regulator or control module.
My reasoning against the sensors is that there is nothing in them that turning the key on would do that wouldn't also happen if you were cranking the engine for that same amount of time.
Another way to test if it was a control issue would be to bypass the pump controls, for that you need to find the condenser that is on the fuel pump lead it is at the back of the engine compartment and will have a black wire with yellow stripe and a black wire. If you pull the connection and jumper battery voltage to the black and yellow wire it will power up the pump. If you do that in the way that it normally doesn't start and now it starts without the 5-10 second pause you have a lack of pump control signal. That could be a bad ECM or bad pump relay. Just more free testing to track down an issue.

It is a returnless system but it still has a regulator. The primary is in the tank with the pump while the other is what Nissan calls a damper assembly. Looks like the item below.