From comments, these are the two options
Use Iconize, as suggested by Carl Lange, which I think is a better option, since you still see the LHS of the assignment and so know what is one that cell, as compared to open/close the cell, where you'd have to open the cell again to see what is there.
In the OptionInspector, you can set EvaluationCompletionAction to "AddTimeStamp". This prepends the Date and Time to all In and Out cell labels. This is almost what you want, but requires some post-processing - subtracting the innie from the outie to get the elapsed time. This can probably be automated.
If the corruption is minor, you can run the restore utility and follow these directions: Link to Restore discussion
However, sometimes that won't work. As a last resort if you have to recover at least some of the contents of your file, you can open it as a text file and excise a complete cell component (with ...
Assuming that the workspace is setup correctly for the Workbench.
File->New project, Choose Mathematica Project
Choose a Basic project (Or Application Project) Give it a name. This name will show up as the name of the container later. I have named it "test" inside the workspace\Base folder.
After the folder structure is in place, right click on ...