It may happen at sometimes that on launching the software, it may take couple of minutes more to display your system drives or connected external drive. However, there are several reasons that are countable for this slowness such as aging of partition or drive, creation of bad sectors on drive, creation of too many partitions, collection of larger amount of data, etc.
What actually happens?
Whenever you run the software, it starts to scan sector by sector to display all the drives loaded with its data. Suppose a hard drive contain bad sectors, in that case due to sector by sector scan software takes few extra minutes than the normal time to get scan the bad sector which results in delaying of drive display.
Moreover in case of USB / External drives, it is normally seen that even operating system takes time to load the drive, as external drive need to get synchronized with the operating system. Hence it goes same with the software that it takes bit more time to display external drive. However, most of the time, this extra time is negligible as it is built in with advanced scanning algorithms.
Some useful tips…!