The time required to move an existing database to Hyperscale consists of the time to copy data, and the time to replay the changes made in the source database while copying data. The data copy time is proportional to data size. The time to replay changes will be shorter if the move is done during a period of low write activity.
A 340 GB database can be migrated in 20 minutes on a Hyperscale Gen 5 80 vcores.Read here.
Hyperscale is capable of consuming 100 MB/s of new/changed data, but the time needed to move data into databases in Azure SQL Database is also affected by available network throughput, source read speed and the target database service level objective.
We recommend you make a copy of your database and migrate the copy to Hyperscale.
In addition, be aware of these limitations on Azure Hyperscale.