There are rumours of changes to the backstop coming from Germany and The Netherlands, but Dublin won't want to give an inch. Although the DUP are saying that the backstop has to go, I think a legally binding time limit would be enough to get their votes.
I think the DUP position is that any one of the following three changes would result in them backing Mrs May's deal:-
1 scrap the backstop
2 put a time limit on the backstop
3 allow for the unilateral leaving of the backstop