I think some of the comments so far in this thread would be considered fairly ignorant by top ICCF players. Personally I don't play serious CC any more and for 3-4 years I did not play at all. Lately I have had some interesting games where the engines don't always find the best moves. Also some games I won ridiculously easily because the opponent either didn't use an engine or didn't know how to use them properly.
Certainly 2 seconds or even 30 is rarely enough time to get a correct evaluation and main line unless the position is so clear that an engine is hardly required. That might be sufficient time for spotting blunders but not for proper analysis.
You can expect top players are mostly using two engines to cross-check with their own ideas. Also players with true chess understanding (which generally means players who have reached at least 2200 OTB) can judge what engine feedback is relevant and what is rubbish, and in particular which positions should be searched deeply (overnight plus) and doing it sufficiently far ahead so it's possible to avoid that line altogether if the outcome is not satisfactory.
It is indeed very hard to win games against opponents of a similar standard who also use their engines properly. It requires either a significant advantage from the opening or outplaying them in an endgame before it reduces to a solved 7-man tablebase position. I have won three rook endgames in the past couple of years (two from equal or only slightly advantageous positions) and in each case (Rybka 3, Houdini 4, Stockfish 6) the engines gave unreliable results.
And in complex middle games you frequently get the 0.00 evaluations because the computer cuts from its search some lines that might be promising and instead shows repetitions and perpetuals. You have the initiative but keep seeing this score so you have to look for ways to keep the game going.
From an interview by Gino Figlio with FIDE GM Leitao in 2008:
https://www.iccf.com/message?message=225 I extract:
GFSubmit Most people that criticize correspondence chess after the advent of chess engines suggest that understanding of the game may not improve for the average player by simply using the powerful calculation abilities of a chess engine. How do chess engines help OTB players and do you see any negative influence in their use?
Rafael Leitao: Certainly most people do not know how to use the chess engines in a correct way. Its use can surely be very harmful for chessplayers in general. I think it is very important that you create your own ideas and form opinions about the character of the position, only using the computer to check for obvious calculation mistakes. Also, most engines do not understand positions with material imbalance. Even with computers, one can never be lazy. Properly used, the engines can improve one´s play.
GFSubmit What are the main reasons why most top OTB players do not play correspondence chess?
Rafael Leitao: I believe most professional players do not have time to play correspondence chess. Sometimes the search for the best move can take days (and even then there is no guarantee you will find a proper answer). And I know many players who enjoy the sportive and psychological aspects of the game, that are most obvious on OTB fights. But I believe that correspondence chess can have a serious impact on improving the game of an OTB player.
GFSubmit The International Correspondence Chess Federation (ICCF) does not prohibit the use of chess engines. Are you planning or perhaps already using them to help you with your correspondence chess games?
Rafael Leitao: Yes, I use all chess engines available. The search for the best move, which is what I try when playing correspondence chess, should meet no boundaries, in my opinion. As I said, blindly following the computer suggestions will usually lead to disaster. In the end, the best players will win anyway. I should add, complementing my last answer, that one of the main positive points of correspondence chess nowadays is that it teaches you (sometimes in the hard way) how to use computers to improve your analysis.