I was just curious because I took what was supposed to be my OG two days after because my hydrometer came late. The reading seemed very low, 1.030, and I was hoping I lost at least .010 from the first two days of fermenting. I used Safale US-05 yeast, pitched at around 90 degrees and let it ferment at 68-72 degrees. Desired OG was 1.052. Since I'm using a bucket I'm not able to see any foam, but activity in the airlock started less than 20 hours after pitching yeast.
I don't believe there is a exact formula to calculate this, but I think that 1.052 would take about 4 - 5 days to ferment with US-05, maybe even less in this temperature. Judging by relatively quick airlock action, I would assume the yeast is in good health. Also, it is worth mentioning that the fermentation is fastest in the beginning, just after the yeast is done multiplying.
I would estimate that you can be sure that it was at least 1.040 and your desired 1.052 is quite possible.
Have you verified your calculations for amount of fermentables with some kind of calculator (I use e.g. brewersfriend)? If you have calculated the amount of malt to match your target OG, then there is a good chance you were not off by much.
You are asking about typical fermentation, there is this from UC Davis relating to wine fermentation: http://wineserver.ucdavis.edu/industry/enology/fermentation_management/wine/problem_fermentations.html
Regarding fermentation in beer this article has a graph that shows gravity vs time for 3 strains of yeast: http://www.virtual-labs.leeds.ac.uk/brewing/fermentation/
Given ideal temperature control and nutrition available to yeast you should be able to get fully fermented out in 4-5 days. This is difficult for a home brewery to achieve, but what you have seen ~1052 to 1030 in two days does not seem at all unreasonable to me.