Hi luvtotravel,
The Inter-American Highway is a little bumpy south of Sierpe so plan for about 1.25 hours to get to the border crossing. Crossing at the border can take a while depending on the lines at immigration (sometimes there are bus loads of people and sometimes hardly anyone). Not sure what your plan is but most rental car agencies in Costa Rica won’t let you take the car out of the country. Assuming you have your own wheels, you will have to go through the process of getting your car approved (we haven’t done this so don’t have much info). Not sure the drive time to Boca Chica from Paso Canoas because we’ve also never done it, but we do know that the highway is in great shape on the Panama side going toward David. Best of luck!