The expertise of your surgeon will have a large influence on your outcome. Assuming one or both nerves can be spared, time for the trauma to subside varies greatly. Two men I know recently said their functions were good after 6 weeks, which can be a common time frame, but you'll find many instances where it can be a lot sooner and others where it can be considerably longer.
Dr Stricker of St Vincents Prostate Cancer Centre Sydney recently posted news on his progress with nerve sparing Robotic surgery and Prof Patel who is a world leader in the technique. You'll find useful information on their websites.
Regarding how to prepare and general recovery time: it's important to remain active and keep up physical activity before surgery. Maintain a normal balanced diet, do kegel exercises, cut down on alcohol, no asprin, or supplements that affect blood.
Successful Robotic usually has less general trauma and he should be active within days. Moderate exercise and walking is good, but no heavy lifting or anything overly strenuous for a few weeks. A common problem is for some to think they are completely back to normal within days, and do something counter productive, so DO NOT OVER DO IT.
Viagra (LOW DOSE) or similar is often prescribed to take on a regular basis soon after surgery as it's believed to assist blood flow and healing.