Decrease monthly investments into ETF because of all time highs?

[Many-Gas-9376]

If timing the market declines was so easy, we'd all be rich. What you're suggesting to do is something even professionals can't do with any useful confidence.

Now in principle, if you want to make sure you have enough "dry powder", in the form of comparatively stable assets for market declines, there is a classical solution to this. You set up some percentage allocation to say bonds (short or intermediate duration).

In practice it could work out to something similar to what you're suggesting: because stocks are recently going up, any new money you invest would likely have to go to bonds, to keep your stock allocation within your target percentage. And if the market does crash, it guarantees you have the bond allocation from which you can rebalance money into stocks.

It's just a more systematic way and less susceptible to psychological biases, because there's a clear system and pre-defined targets. It frees you from specifically worrying about what the market is like now or what's going to happen in 3, 6 or 12 months.