Maturity of a variety is often described as early, mid-season and late. Differences will occur between regions but the general rule of thumb that I follow is early - 60 days, mid season - 90 days, and late - 120 days measured from the time of planting until harvest. Potatoes will emerge anywhere from 3-5 weeks after planting. It is important to have frost-free days from the time of emergence until harvest.
Whole seed can be chitted (green sprouted) prior to planting, this will ensure earlier emergence and may allow you to delay planting. Potatoes are heavy feeders, if you have adequate moisture, add 4lbs of a 7-7-7 fertilizer per 25 feet of row. Planting shallow encourages early emergence especially if the soil is cool. This also reduces the occurrence of Rhizoctonia (Black Scurf).
When to Plant?
How warm should the soil at planting time be? The soil temperature should be at least 5°C. Ideally the soil temp at the depth that the seed piece will be placed should be 10°C. It is also very important that the temperature of the seed piece is close to being the same as the temperature of the soil at planting time.