Which one is better? "Estimated time of resolution" or "Estimated time of completion"
When I have to notify an estimated time when a system problem is resolved, which one is better?

1) Estimated time of resolution
2) Estimated time of completion
3) Estimated resolution time
4) Estimated completion time
5) Estimated completing time

Question

Which one is better? "Estimated time of resolution" or "Estimated time of completion"
When I have to notify an estimated time when a system problem is resolved, which one is better?

1) Estimated time of resolution
2) Estimated time of completion
3) Estimated resolution time
4) Estimated completion time
5) Estimated completing time

Answer

The difference between resolution and completion is quite subtle. Resolution if it is definitely a problem, completion if it is more general job. Using resolution is a little more positive, in that it is focussing on the fact that you are solving a problem, but it might sound a little strange if you are not. To me - the choice is yours.
'time of' would refer to a time of day, e.g. 3pm tomorrow.
'time' is a little ambiguous. It could be either the time that it will be finished, as above, or the time until it is finished. 
So 'Estimated completion time' could be '12 hours [from now/the start of the job], or 3pm tomorrow
Your 5) is the only one where the grammar is incorrect.

Answer

I would say something like "the likely date of completion" or "the scheduled completion date".