That depends where it's being sent from and to - any by which method !
3 days
it took about 8 days to reach its destination.
Your answer depends on the destination in Antarctica and whether or not there is postal service -- which is rather seasonal -- to that destination.
Postal mails (even ordinary, Par Avion) may reach fast from UK to Bulgaria. As there are many flights from London to Sofia per day. The question is from which part of UK is the mail and to what destination is to reach in Bulgaria. Overall 5-7 working days would be good enough. Priority and Courier mails reach faster.
A first-class letter mailed to an address within the same mailing district from which it was posted will generally reach its destination in 2 to 3 days.
it took 20 years
6 weeks
In forty(40) minutes you will reach your destination.
2 to 4 days
26 minutes
How long is a piece of string? No time can be guaranteed, the postal service sucks
1 hour