[anoother]

Did you mean to say 'rational' as opposed to 'not rational'?

If time has positive value, then so do objects with time invested in them.

[comboy]

If your time is of any value to you, then you should be willing to pay more for furniture that is already assembled, not the opposite.

I mean unless assembling it is something that you really enjoy doing. So much that you want to pay extra for that pleasure.

[ambivalents]

Only if you value time more than whatever positive value you extract from assembling (and subsequently enjoying/using) the furniture.

[xapata]

Sunk cost fallacy.