How much time software testing takes depends on a variety of factors. That includes the type of software testing deemed necessary, the complexity of the software being built or upgraded and the size of the dev and testing team. Other factors, including the need for integrations, can also play a role.
When you're working with a software developer or software development company to create a timeline for your project, ask about testing. Your dev professionals should be able to recommend what types of testing might be pertinent and how much time may need to be devoted to the task.