Hiya!
Sure, but by the rules, the answer is, "No, you can't"- you can ready an action, but not delay your whole turn.
Actually, by the rules, the answer is, "What does the DM say?". In the DMG, pages 4 and 5, it states multiple times something to the effect of
"The DM decides if, and, or how, something is handled; or if something completely new needs to be made up to handle the situation", basically.
So, there not being a specific "rule" (like Delay), defaults to the rule of "What does the DM decide?". ALL rules (or lack thereof), default to this one, single, simple rule that so-o-o many people seem to treat as "not as official" as the more very narrowly focused rules (re: the list of 'actions' one can do in a round...Attack, Cast Spell, Use Item, etc).
Why is this? I'm not sure. I suspect it's because a lot of folks are used to things being much more binary now a days due to, well, everything. With the whole "Zero Tolerance" stupidity, the run-amok "PC'ing of everything-under-the-sun" (PC as in "Politically Correct"), etc, kids are taught
what to think and not
how to think. We have computers, in particular, where X = Y. Period. No exceptions. Video games have extreme limitations, and players of said games have learned to exploit them (appropriately called, "exploits"...go figure). Gamers quickly figure out that if they "move past the big purple tree, face the other way, wait 5 seconds, then turn around" that the big
Soot Troll of Bengaar will respawn by the old swamp hut. They go kill it, get it's stuff, go back to just past the purple tree, turn, wait, turn back...and go kill the Soot Troll again. Rinse, repeat. This is binary. It will ALWAYS happen. And, funnily enough, when it doesn't, you will literally hear dozens if not
hundreds of players bitching and moaning about how "the soot troll is glitched and the devs are doing nothing about it". When the devs 'fix' it so he doesn't respawn by doing that, said players bitch and moan again about the devs "nerfing" the game and taking away all the players fun.
Anyway, IMHO, a lot of RPG'ers nowadays are falling more and more into this 'binary trap' with regards to RPG's. By their very nature, RPG's are built to thumb their collective noses at 'absolutes'. Nothing, and I mean
nothing in an RPG is absolute. Because of this, as the DMG points out in different verbiage, a DM's job is to fill in the blanks and decide outcomes when needed. How he does this is up to the individual DM; some just say no, some just say yes, some use other rules as is, some modify other rules in the game, some create all new rules from scratch. The point is... the DM doing this is "creating a rule". The rule he creates is every bit as "real" as the ones printed in the book. Claiming that a DM's rule (or ruling) is somehow "against the rules", when the DMG
specifically states that the DM gets to do this as a rule, is not seeing the forest through the trees.
So, is there a "Delay" action? Nope. If the DM says there is a "Delay" action, is there? Absolutely. Is the fact that there wasn't a "Delay" action before, written in the book, but there is now, because the DM decided, somehow "ammunition for an argumentative player"? No way in H-E-double-hockey-sticks.
Ignoring the "the rules say so" argument, there are a number of arguments that I find persuasive, both from the "keep the game flowing" standpoint and from the "in game narrative" standpoint.
I'm just saying, don't count on pming's assessment of delaying your turn to be shared by your DM.
This I agree with.

Don't count on my assessment. Some DM's just don't "get" what their role/job is as DM, or they only "get" part of it. One of the more weighty things a DM has to do is create or otherwise change rules to make his game run better. If a DM doesn't like how Multiclassing works at all (...raises hand... ), he can just up and say "Nope. Banning MC'ing in my campaign". This is a "weighty" decision because it can have serious effects on some players perceptions of the game and/or severely alter plans or ideas they had for characters. But, that's just one of the burdens a DM has to bare. Not having a Delay action covered directly in the rules isn't such a thing, IMHO, and I honestly can't see why a DM wouldn't just shrug his shoulders and say
"Yeah, sure, you can wait to attack later on in the round if you want". That decision isn't likely to 'mess up' much of anything, and certainly shouldn't be something a player quits the game over (or other drastic reaction).
But, as The Jester said (although in different words)... go ask your DM.
^_^
Paul L. Ming