https://technet.microsoft.com/en-us/library/ms714428(v=vs.85).aspx states (emphasis added):

The Invoke verb is used to perform an operation that is generally a synchronous operation, such as running a command. The Start verb is used to begin an operation that is generally an asynchronous operation, such as starting a process.

Therefore, Start-Sleep, which is synchronous, should be called Invoke-Sleep.

It's probably too late to change this, but:

• perhaps an Invoke-Sleep alias could be defined.

• either way, the inconsistency should be documented.