The duration of a domain transfer depends on the extension. Most generic Domain Extensions (gTLDs and nTLDs) are fully automated and the transfer works via authcode; these transfers are usually finished within a week.
You can use this as a rule of thumb: if you initiate a transfer using an authcode, the transfer should be finished within a week, otherwise something might hold up the transfer and it is worth checking the status of the transfer in your account under Pending Actions.
Country Code Domain Extensions (ccTLDs) on the other hand, are completely different. Many ccTLDs have a special unique transfer procedure, involving documents and confirmation. Few can even take up to several weeks.
Exceptions are internal domain transfers from one Octopoly customer to another, those are instant.
If you have doubts about the transfer procedure for a specific TLD, have a look at our domain landing pages. You will find all the important information there. You are also always welcome to contact us.