Do we need to present in US for H4 to H1 conversion


I am working in California on H1B visa. My wife will come here in Mid April 2014 on H4 visa. I got call from consultancy to convert H4 to H1B. As per them , she need to be here on 1st April 2014. Can anyone please let me know, H4 visa holder need to be present in US on or before 1st April 2014. Can she submit document and come to USA on H4 visa somewhere in mid of April?