The transportation systems start an hour and sometimes more before scheduled early entry (thus about 7 and maybe 6:45) on early entry days. Whether you can take the boat depends. It appears that in some of the slower seasons Disney is not running the boats for early entry and thus it will not start until about 8 as it does on non-ee days (but likely to get you there by 8:30); also if there is heavy fog or bad weather the boat may not run. However, do not despair. Moreover, that roundabout trip to Epcot is not necessary. WL has a bus that runs to Epcot that will begin 7 or before on ee day and about 7:30 on non-ee days. Also, there is a another bus that runs from FW to WL to TTC that will start at 7 or before everyday regardless of any ee; thus if you cannot take a boat to MK in the morning you can take the bus over to TTC and then monorail to MK (or to Epcot if you want).