You're welcome.
There is no specified timeframe to use your credits. You decide yourself when and on what posts you want to spend them. The credits remain yours until you spend them.
If you want upvotes from steemvotes.io on your post you do need to submit it via your dashboard, if you don't want upvotes from steemvotes.io on your post you obviously don't have to submit it.
Hope this could clear things up for you :)