Maybe like this:

local p = {}

local function toDHMS(millis)
	local seconds = millis % 60000 / 1000
	local minutes = millis % 3600000 / 60000
	local hours = millis % 86400000 / 3600000
	local days = millis / 86400000
	return string.format("%d:%02d:%02d:%02d", days, hours, minutes, seconds)
end

function p.toDHMS(frame)
	local args = require("Module:Arguments").getArgs(frame)
	local millis = args[1] or error("missing positional argument #1: milliseconds")
	return toDHMS(millis)
end

return p

Put the code for example in Module:ConvertTime and then you can invoke it:

{{#invoke:ConvertTime|toDHMS|23456576210}}

This should give you the following output:

271:11:42:56

Oh, wow. Didn't think someone would actually respond. Thank you!

It actually "works", but it seems to display an error before the converted time. I edited the output slightly to fit my wiki, but that could be why the error displays in the first place.

Yes, sorry, my bad. I just tested this module in the debug console and didn't invoke it from a regular page…

Try modifying the function p.toDHMS like so:

function p.toDHMS(frame)
	local args = require("Module:Arguments").getArgs(frame)
	if args[1] == nil then
		error("missing positional argument #1: milliseconds")
	end
	local millis = tonumber(args[1])
	if millis == nil or millis < 0 then
		error("invalid argument: " .. args[1])
	end
	return toDHMS(millis)
end

Cool, it works! Thanks again.

Another question, any way to hide the numbers if it returns 0?

You just glue the parts together that are not zero:

local function toDHMS(millis)
	local result = ""
	local days = millis / 86400000
	if days >= 1 then
		result = result .. string.format("%dD", days)
	end
	local hours = millis % 86400000 / 3600000
	if hours >= 1 then
		result = result .. string.format(" %dhr", hours)
	end
	local minutes = millis % 3600000 / 60000
	if minutes >= 1 then
		result = result .. string.format(" %dmin", minutes)
	end
	local seconds = millis % 60000 / 1000
	if seconds >= 1 then
		result = result .. string.format(" %dsec", seconds)
	end
	return result
end

Got it. Thank you once again