When would be a good time to invest $30,000?

It doesn't make much difference when you buy into VGT and VOO. Putting your money in right away whenever you get it is the best strategy.

Now. After you choose a stock, keep putting money in every time the index drops.

In a bull market, it would be advantageous to put it all in at once, in a bear market, it would be advantageous to enter little by little and buy when it drops, and in a market crash, it would be advantageous to wait and put in a large amount at the bottom, but no one can predict the future. Do not leave such a major decision to an anonymous post; please establish your own solid principles instead. If you think of doing it like a 401(k), setting up automated trades for a fixed amount on the same day every month is also an option. Judging by how you panicked and pulled everything out during a sharp drop, you do not seem likely to handle volatility well, so an ETF seems fitting. However, buying an ETF does not mean it will unconditionally go up—it will repeat going up and down endlessly—so I recommend thinking carefully and scaling in over time. I also recommend always keeping around 30% in cash just in case there is an unexpected crash.