When to start Timing

Then I'd start working on timing immediately, to get a feel for how long it takes you to solve problems.

That said, you need to also learn alternative approaches to problems - something that will help immeasurably with timing. It's been conclusively shown that if all you do is algebra, no matter how good you are at it, you can't max out your quant score because the questions will eventually get so complicated that you'll run out of time.

There's definitely an adjustment from LSAT LR/RC to GMAT CR/RC, mostly due to the format of the GMAT. On the LSAT you can take notes right on the page and you're reading off of a booklet; on the GMAT you have to take notes on your noteboard and you're reading off of a computer. You'll find there's a definite adjustment period that slows you down, so it's essential to practice on the computer as much as possible. The brain actually processes information differently in the two formats, so transitioning to the GMAT format is likely to take some time.

You can start trying timing from the beginning of your study. And if you feel like you need for time or more knowledge, just focus on that for a while.