Immigration clearance at KIX

i will be arriving at KIX int airport at 2130. How long does it need to clear immigration and collect luggage?
I dont know whether to stay a night in osaka city or proceed straight to NARA. What is the fastest way and how long does it need to reach  Kintetsu Nara from the airport?

Depends how busy it is. 30 - 60 mins. Going to Nara takes around 2 hours.

Going to Nara takes around 2 hours.

More like 1 and a half...

So is it advisable to travel to nara at this time or better to stay in osaka

You wont be getting to Nara until on or just after midnight. Osaka is about 45 minutes, on to Nara is another 45 minutes. I'd extimate an 2230ish departure from KIX.

1.31 travel time if the mentioned person can transfer within 5 min to the correct platform. If not 2 hours around

Sometimes I go through Immigration in 20 minutes, last flight in May this year, it took 1 hour to clear Immigration/Passport inspection as my flight was 20 minutes early and a Philippine Airline flight was 15 minutes late....about 1000 or more queuing before I recall 10 counters etc..one can never predict!...an alternative for you is to book a night at The Nikko Kansai Hotel...it is located in the Airport terminal, about 4 minutes walk from the passenger arrival exit. You can even sleep in as there is no time to check out...then you can leave refreshed the following morning to Nara. I have done this myself several times.

It depends if you happen to arrive at a particularly busy time (multiple big flights coming in). My last arrival in KIX was particularly horrific. I was in line for around 2 hours. My flight prior to that took less than 1 hour to get through all the airport processes.