No. Word Ladder has no timer, and only the daily ladder is ranked. Your ladder and hints are saved in this browser when storage is available.
Take as long as you like. Your ladder and hints are saved, so you can leave and return to the same puzzle.
Switching puzzle asks for confirmation if you have unfinished progress. Free play is not ranked. The daily ladder has its own leaderboard (how the daily scores).
See also What is par. For tips, read the Word Ladder tips and strategy.