Each electronic manuscript handling system typically has a set time frame for each part of the review-revisions process. The systems have default values which, I would assume, are what most journals use. It is, however, possible to custom make the different time periods for each part of the process.
1.Submitted to Journal:
This usually does not involve a lot of time and a reasonable time frame might be
5-10 days depending on factors such as workload, time of year etc. The step might involve inspection of the quality of the submitted material, but not necessarily.
2.Editor Invited (Conditional - this step may not occur):
This may again be another
5-10 days and may be affected by workload etc.
The main problem that occurs here is difficulty to assign reviewers. The editor may also be overloaded with work. The time frame is likely something like
3 weeks but will vary.
Each journal has a time frame and
3 weeks is what I am accustomed to in my field. Reviewers that accept reviews and never return them is a problem here. How quickly the editor tries to assign other reviewers to speed up the process will vary from person to person and journal to journal.
5.Required Reviews Complete:
I am not sure if you actually mean revisions here because typically the author gets about
3-6 weeks to revise the manuscript. This is another point where delays can occur but they are self-inflicted.
6.Decision in Process:
The decision process may require some time since the editor needs to read the revised manuscript and the revisions/rebuttal from the author to make a decision. In many cases there is cause for another round of reviews which would loop back to 4 and 5.
7.Completed – Accept:
7 could be 6 if the manuscript gets accepted after one round (rare in many circumstances).
Once accepted, the manuscript goes to copy editing and type-setting. This may be a quick process depending on the resources provided by the publisher. Journals using LaTeX have the advantage of having print ready proofs basically at the turn of a switch.
To sum up. Each of these steps can take various amounts of time depending on the working conditions at the journal as well as the expedience of reviewers and authors. I think the time frames I have outlined are reasonable but that does not mean all journals will be that quick (or slow, depending on your view).