Transfer time between terminals in Dubai Airport (separate tickets)

Given that your two flights will be on separate tickets/bookings.

In that case:

• You need to:
  • Deplane (can take a good 15 minutes if you are at the back of a 777 or 380).
  • Get to immigration. Dubai airport is large, and some gates require you to take an inter-concourse people mover. I'd count a good 15 minutes for that.
  • Go though immigration. No idea what queue times can be in Dubai, but I'd count at the very least 15 minutes for that, possibly more.
  • Reclaim your bags. We'll suppose you'll have spend enough time getting there that your bags are ready to pick up.
  • Go through customs.
  • Transfer to the other terminal. I'd count a good 30 minutes for that (find and get to the shuttle bus stop, wait for it, ride it).
  • Find and get to the check-in counter for your second flight. 10 minutes.
  • Drop your bags before the check-in/baggage drop deadline for that flight (Air India check-in deadline on international sectors is one hour before scheduled departure).
  • After that you still need to go through security, possibly exit passport control, and get to your gate before the boarding deadline, but in most cases if you met the baggage drop deadline you should be fine for that.

So, if your incoming flight is on time, you have a margin of 30 minutes at best, possibly less. This is really quite short if the incoming flight is on time, it may prove impossible if there is any delay or complication.

• If you miss the check-in deadline, you will be considered a no-show.

  In many cases, this means the airline will automatically cancel your ticket, including any further flights on the same ticket (e.g. a return flight). Unless your ticket's fare rules provide otherwise (usually only on "flexible" tickets), that means you'll have to book and pay for new tickets, which, at the last minute, may be quite expensive.

  If the next available (or affordable) flight is the next day or later, you'll also have to pay for accommodation and meals by yourself.

The usual rule of thumb is to have at least 4 hours between two flights that are booked separately, though depending on the airports, the flights involved, the costs of those flights, and many more parameters, you may want to have a lot more padding.

Since this is between two long haul flights, the cost of the second flight is probably quite high, and you may have to wait until the next day for the next available flight, I would personally have a lot more padding (usually an overnight stay).

Note however that Dubai has a pretty unusual service which can transfer your bags for you, which would enable you to skip immigration, baggage reclaim, and enable you to stay airside (Terminals 1 and 3 are connected airside). This comes at a cost, but would significantly enhance your chances of making the connection.

I would start by using their online form to check availability, and possibly contacting them for confirmation.

Note that this doesn't solve the issue of your first flight being severely delayed or cancelled and you still missing the second flight, it just increases your odds of making it in time (and makes things a lot easier as well).