If you want to enter US earlier than 10 days then you have to apply for B-1 visa. During entry to the US on B-1, the I-94 validity will be up-to the duration of the visa. However, you cannot work using that visa. To change status to H-1, you have to travel abroad and get the H-1B stamped (skip this step if already stamped) and get a new I-94 (during re-entry) based on H visa stamp.