If they are the run of the mill Tiger Lilies that grow everywhere then move them whenever you want. They might wilt for a day or two but I bet they come back. You can't kill those things anyway.
Make sure you dig down far enough you get all of the corm or you will be getting mroe growing in the exact same place you are trying to move them from. They are a biatch to get rid of. Just warn you - use a strong shovel. It ain't easy.