This is non-negotiable! That’s how it works and nothing else.
You say that you have already tried 3 times: have you been patient enough? The first thing that happens is that, in the background, a list of all tasks is being constructed. You don’t see anything happen during that time, but you should not interrupt it and just be patient.
Depending on the number of activities that needs to be imported, the entire process can take more then 24hr.