The time required to backup Altaba Mail completely depends on the internet bandwidth. You can set the internet by throttling in Yahoo Mail Backup software.
No, it is not possible to backup more than one email to another format at one time in bulk using Yahoo Backup software.
No, by using Yahoo Backup you cannot move contacts from Yahoo. The software can only export emails from Yahoo Mail to Outlook PST.
Yes, you backup Yahoo Emails to hard drive using Y Mail Backup. You just need to provide the desired location during the conversion process.