If you have bought your preorder of Grand Theft Auto V from Rockstar Warehouse of Steam you can start preloading on April 7th. The information comes from the FAQ section on Rockstar’s support site.
Though the April 7th preloading is only for those who purchased from Steam and Rockstar Warehouse. As on the support page it says “If you pre-ordered GTAV from a digital retailer other than Rockstar Warehouse or Steam, please contact your retailer’s customer support departments for details on pre-loads.” Preloading will definitely be needed if you want to play the day it releases since Steam has put the minimum hard drive space requirement at 65GB.
