i can't start missions at the same time/in a hour

1) do you have enough mission slots unlocked?
2) are the new missions you are trying to get different from missions you already have active in your mission log?

1) yes
2) no

if 2 is no, then it's a simple matter- you can only have one of any given mission at a time- they cannot double up. You can't have, for instance two of "An Ox at Heart" (Esior lv25/Very Hard Dex mission) in your log.

oh, okay