Effectively, no. It's more complex, but the real answer is that your readied action is to roll initiative, possibly taking your surprise round (or not)
Sure, you could go this way. Since you are not in combat though, 85% of the combat rules and arguments are thrown out. Out of combat, PC's are a little more free to do things. I see no problem with your character making a plan, and following through, *before* initiative is rolled:
"I suspect there is a guard in that tower. I have now managed to stealthily sneak to it's base. I am currently climbing the ladder. Once I get to the top and peek over, I would like to toss my dagger at him"
That is a good application of the Surprise Round. How about:
"The Wizard cloaked us all in invisibility. We rounded the corner and saw three Hobgoblin guards sitting around a table playing cards. I would like to sneak into the room and light the table on fire. In the ensuing commotion, we should have an advantage in the fight."
So the rest of the party cannot ready an action for when they see the table go up in flames? Because we are not in combat? Clumsily modelling this as a combat is silly (roll initiative, go by rounds, but since the Hobgoblins are unaware of the PC's they do nothing on their runs) when you could allow this stunt to be a moment to remember.
I say outside of combat readied actions are fine. In the above case, everyone is waiting, tensed to pounce, and when the oil flask hits the lantern in the center of the table, they attack. Not, they roll initiative, and get one action, they attack. They get their readied action, then combat as normal.
Yes, the distinction is small, but to me it is real and I am allowed to be cranky about it. Like Santa Claus.
Jay