Tim started making crosses in California in 1996, but before then he took a year out to travel the world looking for potential parent varieties from countries as far as Australia and Azerbaijan. Tim assembled a collection of some 200 diverse parent varieties. Each one was chosen on the basis of certain unique characteristics that Tim and SNFL wanted to see in the final new varieties. Attributes such as flavor, crispness, and berry size were the main priorities.
Tim made over 300000 crosses over the next few years and generated over 30000 seedling vines which had to be planted out for detailed evaluation in test fields in California, Arizona and at SNFL farms in Spain. By 2005 this work was beginning to show results and the first new seedless varieties from the Sheehan programme were being planted around the world. These plantings include some of the first varieties to emerge from the programme such as Timpson, Magenta, Timco and Allison, and later introductions such as Kelly, Krissy, Ivory, Great Green and Melody.