Sign up for Office 365
Learn more about Office 365
Thank you for your post.
The time taken by migration process can be related to various factors, for example, the size of mailbox, network bandwidth, performance of exchange server in on-premise domain.
However, for your situation, since there are only 4 mailboxes (3 mailboxes and 1 public mailbox) need to be migrated, you can migrate the emails for users by exporting/importing .pst file referring to article below.
Use Outlook to Move Data Between Accounts
By the way, if you would like to migrate mailboxes for users with Staged Migration, please following detailed instructions in following article to do it.
Migrate a Subset of Mailboxes to the Cloud with a Staged Exchange Migration
The speed of your migration depends on many factors: network speed, network latency, number of mailbox items, size of mailbox, number of errors, and server load. blog.migrationwiz.com/.../how-long-does-it-take-to-migrate-a-mailbox
I would not recommend using the PST export/import method because the emails would be unrepliable at the end user. Also, this is a very long process that requires constant monitoring.
I don't see any comments since the prior post. Did the above replies answer your questions? If the information is helpful, please show this thread as answered so others may benefit from the information. Thank you.