Any system where management writes a schedule and hands it off to programmers is doomed to fail. Only the programmer who is going to do the work can figure out what steps they will need to take to implement that feature. And only the programmer can estimate how long each one will take.
Design first, and in detail
Attempting to estimate a feature before you’ve figured out how the feature is going to work, in detail, can’t possibly work, even if you “multiply your best guess by three,” because your “best guess” is based on very little in the way of facts. The nature of software development is that things which seem simple are often surprisingly complicated when you think about all the details. For example, when you think about creating a registration and logon system, you might forget that you’re going to need a way to prevent passwords that are the same as the user name, and a way to deal with forgotten passwords, and a way for people to unregister, and so on. Until you try to figure out the design of all these things, you have no basis for an estimate at all.
