I know that you can have Excel insert the current date with CTRL + ; and the
current time with CTRL + SHIFT + :. Is there some way to insert both with
one command?

I know it seems like a small thing, but we have a worksheet for employees to
keep track of completed tasks. When they complete a given task, they need to
put the date and time of completion in a specific cell. However, over the
course of a day, they may be completing upwards of 250 tasks. Even lessening
the time to complete the time stamp by a single set of keystrokes would be
helpful.