I usually do set up a Single Player world for the sole purpose of gathering lots of TIme Chrystals (TC). After having done it with three or four worlds now, I’d like to share my experience. You will easily be able to get 1000s of TCs.
Warning: I do use jetpacks, lanterns and titanium picks warped in from my main world to speed up the process. If you can’t rely on such resources it will take you much longer to raid the whole world.
Start a new single player world and get a Portal Chest asap.
Circumnavigate the world. This will later help you when you are down underground, as you can see in zoomed out view how deep down you are and wether you are underneath an ocean.
By this time you will have warped in useful stuff like lanterns, pickaxes, pole items from one of your other worlds. Start mining straight down until you find a cave.
Follow that cave. I use a mix of steel lanterns and oil lanterns, depending on what my main world is able to deliver. I make a habit of placing the lanterns as far as possible ahead of me into the semi darkness. Usually thats like 14 or 15 blocks ahead. Whoever is more anxious might want to place lanterns at 8 blocks intervals, as you are less likely to run into a cave troll or a body of water.
TCs are to be found in caves. In two years of playing the BHs I have only ever found 1 TC block completely enclosed by stone.
Mine every TC block you find using a diamond pick. As most of you will know this adds 18 TC to your overall TC count as opposed to only 3 TC when using a normal pickaxe.
Most caves will lead into a large system of caves. Follow every single “side street” until you have lit the whole cave system and mined all TCs in it. Sometimes a cave will fade out into a series of unconnected small cavities.
Don’t let this put you off. Grab your pickaxe and mine your way along them. Often this will lead you to another open cave and some TC blocks.
When you get to a “dead end” and you can’t see another cave within the range of the light, place 3 lanterns side by side to broaden the range.
When you get to a junction, choose one way. But go a little bit into the other way too and place a lantern. This will later enable you to easily spot any still-to-explore “side streets” in zoomed out view.
When you’ve only got dead ends and can’t spot any more cavities to explore, its time to dig a shaft to find a fresh cave system. As you can see on the picture I prefer digging vertical whenever possible as this is really fast with a jetpack and titanium pickaxe.
Digging horizontal is awful slow in comparison.
While mining your way through the world, you will encounter two major hazards: cave trolls and water. How to deal with trolls has been discussed in length on this forums. But what about the water? You might accidentily dig into an ocean or an underground river. The water will wash away oil lanterns and threaten to drown your BH in the dark. Not a situation you like to be in! So what to do to avoid it? Use steel lanterns. They are waterproof. And whenever the zoomed out view gives you reason to suspect you might be near to water, build a water barrier like this.
It will hinder the water from flooding large parts of your cave system. Dont be afraid to explore underground rivers, you will often find TCs and gems under water.
So you are asking how many TCs you can expect on any Single Player world? On one of my worlds I actually took notes of every TC I got and every troll I found. The total net score was 10,622 TCs and 22 trolls, 11 of them equipped with a trade portal.
So taking into account the -520 TC I started with (needed to upgrade the portal and make a portal chest) I actually got 11,142 TC out of that particular world. That equals 619 TC blocks found. Of course the result depends on how tight you draw the “grid” of your shafts and explored caves. The picture shows how I typically do it. There might be a few more caves hidden in the black patches, but I don’t feel its worth the time to find them.