I tested program launch times with AppTimer when deciding for Windows defender on Windows 10. In the end the first uncached launch of a program is the slowest part on most PC's.
You can set up a task to schedule the update, for example every hour
Updating WD signatures in this way, would be advantageous only when working offline with unsafe content. When online, WD uses 'Block at first sight' feature, which has malware fingerprints long before the signatures will be created for them.You can set up a task to schedule the update, for example every hour
Update Windows Defender when Automatic Updates is disabled