Begonias from corms

I am going abroad for 7 weeks and would like to start my begonias off before I go away.  What is the best way to do this?  Shall I put them in trays in the greenhouse (unheated), or in trays on a window sill (there will be someone at home to water occasionally if necesarry.  Approximately how long should it take for leaves and roots to sprout?  Would it be better to not bother at all and wait until the end of March to plant when I will be home again?  I would be very thankful for any advice here. 

you can leave till the wnd of March then start them off in trays or pots, or you could leave them in a trays on a window sill, not near a radiator or where the spring sunshine may burn the tender shoots keep the compost slightly most until leaves appear .

Thanks Philipgardener.  Could you give me an approximate amount of weeks it may take for the shoots to appear?