Potential problem with new Essence Reaver

I really like the new essence reaver changes but I feel they are going to need to be fixed for some marksmen. You get a buff after casting your ult. After casting your ult you have 10 seconds to do a basic attack and get the buff. So what about the champions like lucian and mf who have ults over time? I feel that the 10 seconds will start as soon as they start their ult which won't give them much time if at all to get a basic attack off. I feel the 10 second window needs to start for them after their ult is done.