Fraction of a second. I would still see if Macrium has a desktop product that will back up SQL. Maybe you can run Macrium Server on Windows 7 Pro. Most of the higher end versions of backup software will back up SQL continuously or near continuously. Every one to five minutes. In seconds. And, it takes up way less space.
For instance, I have five days of AC SQL backups every 15 minutes which ends up being 48 backups a day (only do 7 am to 7 pm) = 240 complete backups of SQL's .mdf and .ldf databases. That is 5GBs. Where just the actual databases are more than that. And, it's automatic. Constantly backing up daily and being backed up the right way. (Not that your way isn't).
And, if you're worried about what the others have said about data losses, etc., back up the .ldf files. No big deal.
