From The Jargon File (version 4.4.7, 29 Dec 2003) :
tube time
n.
Time spent at a terminal or console. More inclusive than hacking time;
commonly used in discussions of what parts of one's environment one uses
most heavily. ?I find I'm spending too much of my tube time reading mail
since I started this revision.?
From The Free On-line Dictionary of Computing (30 December 2018) :
tube time
Time spent at a terminal or console. More inclusive than
hacking time; commonly used in discussions of what parts of
one's environment one uses most heavily. "I find I'm spending
too much of my tube time reading mail since I started this
revision."
[{Jargon File]