I'm not sure if this is a question about timing but more of a behavioral question.
The odds say putting a lump sum in sooner than later it the best option since the market (not sure which market but let's say sp500) goes up more often than down.
But catching one of those down days/weeks/months can lead to buyer's remorse which could color one's investing behavior going forward.
Therefore I agree with Burton Malkiel that DCA'ing may be the preferred method (much like Ramsey's debt snowball method, it is not mathematically optimal but may be psychologically).
So rationally we should put it in up front, all at once. Emotionally, we may want to wait for the optimal time to let those dollars enter the market. Perhaps one method is to split up the $5500 into 12 months ($458.33/mo) and set a rule for deviating from equal payments (unequal DCA). It might look like "If the index goes down put in 2x percent more than the change in the index. Make no change if the index goes up."
It might look like this:
Mo0: $458
Mo1 (index goes down 5%): 458*1.1=$504
Mo2 (index goes up 3%): $504
Mo3 (index goes up 2%): 504*1.04=$524
Whatever mind tricks you have to do. In this example scheme, on a short term minded basis, you ratchet up so at least you feel you are buying more shares than the prior month. Does it matter in the long term? nope.
In my case, I don't like tracking my contributions so I like to throw it all in on Jan 1.