i left my sprouts for 10 days... they got fucked.. took 2 weeks to un-stunt them... but 4 days shouldent be a problem at all... i normally water every 4th day... so... just water alot befor you leave... try to increase humidity in the room befor you go( so soil stays moist longer) and raise the lights a little bit so your plants wont overheat if they do get low on water( althou they shouldent) and you should be fine