killing time; passing time
Neutral or slightly positive: doing something to fill spare time, similar to 暇つぶし.
See also: 暇つぶし
I killed time on my phone while waiting.
I brought several books to pass the time on the long flight.
wasting time; waste of time
Negative nuance: spending time unproductively or on something pointless. Often used in phrases like 時間つぶしにしかならない.
That meeting was a complete waste of time.
Just playing games all day is nothing but a waste of time.