| Allergic contact dermatitis from urushiol contact (aka you got hit by poison ivy) is interesting. I've read where the urushiol oil bonds to the skin in as alittle as 3 minutes - here's the reference for that information:
http://res2.agr.ca/ecorc/poison/symptom_e.htm
Now washing helps to minimize the the amount of exposure and washes off any urushiol which has not yet bonded. So you've done the right thing.
The rash won't always appear all at once. There are many factors involved including where the contact occurred, how much exposure, etc. So it's not unusual to break out in rashes over a period of time. Places where the skin is thick like the palms are not likely to break out but thinner spots like inside elbows, wrists generally break out much faster. It may be that you are seeing all of the areas where you were exposed to urushiol just breaking out in a rash over time.
The other possibility, though not likely unless this is a very severe reaction, is that this is systemic. In that case you will pop up with rashes in places you don't expect over a period of weeks. If this is the case and you have a systemic reaction, you should go see your doctor.
From what I understand, once the urushiol has bonded to the skin it can't spread. The oozing from the blisters is your body's reaction to the urushiol and there is nothing to spread. You're doing the right thing by keeping everything clean and dry. Unfortunately, you'll have to bear with this for anywhere from a week to a few weeks. I've been there - it's not fun. | 
