There's a large difference between criticizing the timing of the lawsuit and criticizing the notion of the lawsuit.
Filing suit against the Administration because members of congress feel they've overstepped the bounds of the constitution is ABSOLUTELY a reasonable notion and one that we shouldn't just want, but demand, out of our various branches of government. Part of the largest job that the various branches have is to act as checks and balances. The President has exercised some of his power to "check" congress by using signing statements to denote things that are unconstitutional in his opinion, for instance. The Congress should be exercising theirs by bringing suit on issues they feel the President is acting unconstitutionally in their opinion. Which allows the judicial branch to exercising theirs by judging the constitutionality of the actions. There is nothing condemnable with regards to that general notion.
Waiting till you're less than half a year out from the next election to finally actually exert your "check" however is something that can be reasonable condemned. As I said....IF the republicans, and others, in congress have had such issues then its incumbant on them to **** or get off the pot. I think they should've **** a lot earlier than they are, but I am in general happy to see that they're finally going to do one or the other as opposed to just staying on the crapper.