Timing on treating mash water

Simple question - how long do I need to wait after treating my mash water before I use it? In other words, after adding my adjustments, (usually gypsum for hardness and citric acid to lower the Ph) can I use the water right away or do I need to wait a certain period of time?

There is no accepted right or wrong answer to your question.  Some people add the water salts just before doughing in and some (like myself) add them well in advance to allow them to dissolve completely. 

If you are relying on the acid addition to be your main pH control and the Calcium sulfate to enhance the finish of the end product, then adding them just before doughing in would work fine. 

My personal experience is that I get more reliable and repeatable results when using the salts to help with pH control to add them in the night before and allow them to fully dissolve before the addition of grains. 

Just to add to what Oginme said, I have good results stirring salts into the grains prior to doughing in and acid additions to the strike water as it's heating. I used to dump salts into the MLT before the water, but thought they might not be evenly distributing.

Do you get any citrusy flavors/aroma using Citric acid in beers that these flavors are out of place? I've often thought of trying it in place of Lactic acid. Just never got around to it.

Things I've done in the past is to mix up my salts in a flask on a stir plate, then pour into my water. I always recirculate the water for a "good amount" of time before doing anything, usually the whole duration its heating i've got it whirlpooling.

I've found once before when adding salts directly to my water and just stirring by hand it doesn't dissolve properly, as evidenced by a couple of rust spots that occurred on one of my kettles that looks like it was probably due to some salts sitting in one spot.