Unless you really want to stop over, that distance is easily achievable in one day. In years gone by, before the road network was as fast as it is now, and when it was cost effective to drive from Malaga to UK, I used to get across the border into France in one day
http://www.distance-calculator.co.uk/distances-for-estepona-to-bilbao.htm
Distance Calculated from Estepona in Spain to Bilbao in Spain
Approx distance in miles from Estepona to Bilbao is 484 miles or 778.76 KMS 
This page was designed to give you a good indication of the distance from Estepona to Bilbao. Distances from Estepona to Bilbao are a rough measure only showing the shortest distance as the crow flies, using longitudinal and latitudinal points. The Estepona maps link here gives driving directions and may be a better indicator of the distance between.
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By Road: If you were in a road vehicle maintaining an average speed of 40mph (64 kmh), it would take you approximately 14.76 hours to travel from Estepona to Bilbao for an estimated driving distance of 624.36 miles (950.09 kms) . (see map below for precise driving times, directions and distance)
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Average Speed
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Overall Estimated Drive time
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40 mph
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14.76 hours ( minutes)
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55 mph
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10.74 hours ( minutes)
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70 mph
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8.44 hours (415 minutes)
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