Testing Water Parameters?

Just a quick question, just wondered how long do you leave after a water change to check your water conditions again?

 I've been having issues with our tank after we had a slight misunderstanding leading to all parts of our internal filter system being cleaned all be it in old tank water but still almost killed all our fish . Due to this I went and bought a big external filter (JBL e1501) this has brought its own issues having to cycle it with already stressed fish is not a fun game for anyone least of all my poor fish.
So I got the external on 5th may and we are still struggling with massive spikes of ammonia,nitrites,and nitrates. I have been doing small water changes every 3/4 days but last night when I checked the water everything was off the charts again (see below) so I've done 2 fair sized water changes in the past 24 hours amounting to probably 80% ,all fish are healthy looking and swimming around  no sign of burns or breathing issues so I'm guessing they are fine at the mo. My fish range from fairly old silver dollars (7yrs ish) to fairly young severums,clown loaches and rams. no water issues before this.

Before water change using nutrafin testing kit,note these were all on the way down a few days ago.
ph.7.5
ammonia 4,9
nitrtites 1.6
nitrates 50

But I just wanted to know how long would you leave it to check the water again?
Thanks in advance .

You can check the parameters half an hour after a water change, that allows the new water to mix thoroughly. If the water change has not reduced ammonia and nitrite to virtually zero, another water change is needed straight away.

If you show any reading for ammonia or nitrite above zero, you need to do a huge water change. By that I mean 90% plus for readings as high as yours have been. This is quite safe provided you get the new water the same temperature as the water already in the tank. Doing 2 40% changes is not the same as one 80% change as the second 40% one removes 40% of the new water from the first one.

The reason you are seeing the amount of ammonia and nitrite is because you are doing a fish-in cycle. You may be removing the chemicals with water changes but the fish are continually making more ammonia and now that you have some ammonia eating bacteria, they are continually turning some of  it into nitrite. Ideally, you should be doing around 50% changes every day. Maybe more if the ammonia or nitrite readings go up fast.

Your ammonia had dropped by half after the water change. It is possible that your nitrite had dropped as well but after 6 hours more of it had been made. Nitrate is very difficult to make home test kits for and only gives ball park results at the best of times. I assume the Nutrafin kit has 2 or even 3 bottles for the nitrate test, and that one of those bottles has to be shaken very hard before use. Have you been shaking it like the instructions will say? All the liquid reagent nitrate testers have one bottle with a reagent that settles on the bottom of the bottle. All the shaking is necessary to get it back into the liquid.

I would leave the filter alone until after the cycle has finished. The most I would do would be to empty the water out, but that shouldn't be necessary. Don't touch the media just yet, you don't want to do anything to disturb those growing bacteria colonies.

another quick question, would using ammo lock help or hinder do you think?
I thought it'd help the ammonia obviously but will it kill or affect the bacteria?