He , meanwhile, whatever he might feel, acted with all the firmness of a collected mind, made every necessary arrangement with the utmost dispatch, and calculated with exactness the time in which she might look for his return. (Chapter 43)

The clock struck eight. Had it been ten, Elinor would have been convinced that at that moment she heard a carriage driving up to the house… (Chapter 43)

…for within half-an-hour after Willoughby's leaving the house, she was again called down-stairs by the sound of another carriage. (Chapter 45)

I agree with all you say and would add a little. I think Elinor was anxious to get rid of Willoughby because although he agreed to be less violent and quick it seems that his imposition on Elinor’s time might have been up to one and a half hours. Before leaving for Barton Cottage Col Brandon calculated exactly when he would return with Mrs. Dashwood. When Elinor thinks she hears the first carriage she is sure she is wrong because they would be two hours sooner than forecasted by the Dear Colonel—ETA is apparently at 10 o’clock. When Mrs. Dashwood and the Dear Colonel do arrive it is only 30 minutes since Willoughby left so if they arrive at 10 o’clock as predicted by the Dear Colonel then Willoughby, who arrived at 8 o’clock, stayed for an hour and a half till 9:30. If Willoughby had an hour and a half to work on Elinor feelings I guess it is no wonder she is taken with his charms again—at least she understands his person and manners have swayed her opinion. (;D)