[Pollard]

Once a bill gets to the president’s desk, is there a time limit for him to sign or veto it? If not, he could hold off until after Kavanaugh is confirmed and then veto. He could also do a line by line veto.

[Buckeye McFrog]

He could also do a line by line veto.

No, he cannot. Line item veto was overturned by the Supreme Court during the Clinton administration.

[Repeal The 17th]

“... is there a time limit for him to sign or veto it? ...”
A bill does not require a presidential signature,
but 10 days are allowed for a presidential veto.

“... also do a line by line veto ...”
No, there is no such thing.