The Scottish government says it will take until March 2016 for Scotland to become independent if there is a "Yes" vote in the referendum in autumn next year.
First Minister Alex Salmond said the timescale was in line with previous international experience.
He told BBC Scotland: "30 countries have gone through the process of having a referendum and then becoming independent.
"The average timescale for these 30 countries since the Second World War is 15 months - we've actually allowed a bit longer than that in the process."
Mr Salmond then asked: "If 30 other countries managed to do it, then why couldn't Scotland?"
The Scottish government has given the BBC a list of the 30 countries which it says have decided on independence since World War II - along with the year they took UN membership.
- 1960 Central African Republic
- 1960 Chad
- 1960 Gabon
- 1960 Dahomey (Republic of Benin)
- 1960 Upper Volta (Burkino Faso)
- 1960 Togo
- 1960 Senegal
- 1960 Niger
- 1960 Mali
- 1960 Malagasy Republic (Madagascar)
- 1960 Ivory Coast
- 1962 Algeria
- 1962 Jamaica
- 1975 Comoros
- 1976 Samoa
- 1977 Djibouti
- 1980 Saint Vincent and the Grenadines
- 1981 Vanuatu
- 1990 Namibia
- 1991 Estonia
- 1992 Croatia
- 1992 Slovenia
- 1993 Eritrea
- 1993 The former Yugoslav Republic of Macedonia
- 1994 Palau
- 1999 Kiribati
- 2000 Tuvalu
- 2002 Timor-Leste
- 2006 Montenegro
- 2011 South Sudan