Queue Time is the time an item waits in queue at a work center before they start working on it. Possible reason for waiting:

a.

All of the options

b.

Need to fulfill a minimum number of units for processing

c.

Items waiting in line for their turn to be processed

d.

Wet product needs to dry completely or, hot product needs to cool down, before it can be processed next

e.

Product awaits approval from quality supervisor before it can be cleared for next stage