What is the best way to start earlier, or have the full invastion happen later?

[Praevasc]

I'm planning a run with brutal AI and playing it very slowly and carefully, without savescumming, on a lower difficulty, but that will give me fewer missions overall and I risk falling behind.
The problem with easier difficulty modes is that events don't happen as often, so there are fewer occasions for gathering crucial loot and crucial prisoners. Especially if I don't reload if I failed to capture a cult leader alive, and have to wait ages until such a mission appears again. And upping the difficulty with brutal AI would make it even more problematic.

What is the best way to have more time before the invasion, besides editing my savefile every month and setting back the date and monthsPassed?

It would be even nicer if there was an option to set the starting date, or the invasion date.

[Kozinsky]

You can use a submod that delays the alien invasion by a year (or two or three):
https://mod.io/g/openxcom/m/start-early-for-mod-x-com-files

As far as I know, this submod mostly works as intended, but maybe some events and missions are still not affected like the rest. This is especially true for the latest version of XCF.

[Juku121]

Aren't the only events/missions that difficulty affects in XCF shootdown-based retaliations? The problem with higher difficulties is inflated enemy counts/stats, which can be real trouble with BOXCE. Well, that and generally getting less loot and XP. But not missing out on anything as such, beyond the normal RNG lottery everything comes out of.

[psavola]

I think what the OP was referring to was missions that have fewer enemies, including leaders and commanders you need to capture to unlock the next level of missions. If there is only one and it gets killed, you're worse off than with, say, superhuman, where you might have 1-3 of the same enemy leader/commander type in the mission.

I guess this could occur a couple of times with the first four cults, but I doubt its impact on the timeline is all that significant - also because the start of the invasion is usually rather slow. If the RNG is favorable to you, you can complete the whole game by the end of 1999, I think.

[Praevasc]

I did a playthrough with the 2.2-2.3 versions, and my problem was that as the end of 1998 approached, I was woefully unprepared. Having fewer progress-critical missions, and not savescumming if I fail to capture the target alive, really hurts. Also, as I have to play hundreds of standard missions, even playing very carefully, occasional mistakes (or extremely bad RNG) do happen, leading to a lot of attrition, slowing my progress even further.
And I prefer to dive into the game (and new updates) blind, without too many spoilers about what I should be focusing on or preparing for.

[Stone Lake]

The game became much easier since 2.3. You don't need any mods to have a relatively chill time in 1999.

What is the best way to have more time before the invasion, besides editing my savefile every month and setting back the date and monthsPassed?

Why edit it every month? Edit it once per year or the like.

I did a playthrough with the 2.2-2.3 versions, and my problem was that as the end of 1998 approached, I was woefully unprepared.

And I prefer to dive into the game (and new updates) blind, without too many spoilers about what I should be focusing on or preparing for.

You wanted to be unprepared, but you got to be unprepared? I fail to see the problem.

It's the intended XCF experience, actually. You're not intended to prepare for anything (or be at specific tech level at any point) - to compensate, the game is made to be nearly unloseable, as long as you don't give up and still have some funding.

Having fewer progress-critical missions, and not savescumming if I fail to capture the target alive, really hurts. Also, as I have to play hundreds of standard missions, even playing very carefully, occasional mistakes (or extremely bad RNG) do happen, leading to a lot of attrition, slowing my progress even further.

Again, fail to see the problem. Why does "slowing progress" even matter? You can beat aliens at lowest tech available, albeit with casualties.
Then, you chose to play it like that. The options are: 1) blind 2) ironman 3) smooth & comfortable campaign - you can only pick two.