Leave preamp on all day, off at night

Since you haven't said what preamp you are using any answer may or may not make sense.  If you have something with 10-plus tubes, then the above answers may apply.  However, if you have something with a pair of 12ax7, 12au7, 6922 or similar, then leaving them on 24/7 really won't make a difference (other than shorter tube life).

As an aside, if you truly love your wife and children would you really limit them to a Bose system?  In most states that would be grounds for divorce.

Most of the comments above, heat, aging, etc., apply to both SS and tube electronics. Preamp tubes don't get too warm as compared to amplifier power tubes so the only real difference between an SS and a tube preamp is aging of the tubes and that's part of the ownership experience. Besides, regular/OEM tubes are not that expensive so I wouldn't worry too much about it. That said, personally I think it's a waste to use a piece like an ARC Ref3 for an all day background music purpose but that's just me.  

I have several preamps.A later ARC with expensive tubes requiring replacement at 2000 hours/4000 hours, leaving it on all day is only 16 months to 4000 hurs. 8 hr day. a 12 hr day would be one year!A more typical 12 AX7 AU7 setup the 24/7 on tubes will last about 4 years to 5 years. Since 12's are cheap tubes.. less of an issue.

I suggest using a second preamp, Solid state for 24/7. saving your better preamp for 'critical' listening. Get one with a HT bypass, so it can be easily toggles out of the system when you use the tube preamp.

I do that with CDs/SACDs I listen to a $40 changer to my $$$ DAC all the time. Saving the $$$ spinner.

You did say what preamp and I missed it.  Sorry.

Tubes should warm up in an hour or so.
So, I would turn everything off when done for the day.
B