Lawn treatment and when to overseed?

Hi all,

2 weeks ago I used "Evergreen Complete" on my lawn in an attempt to tackle some of the weeds.

It does not seem to have made a huge difference apart from turning a couple of them brown/black - certainly not the majority.

My questions are:

1. Should I wait a little longer or use an additional treatment for the weeds in the grass? Any recommendations?

2. I need to scarify the lawn but suspect I'll need to overseed after; the Evergreen Complete and other forums have mentioned not to put new seeds down as they'd be killed, can anyone advise how long I need to wait? (My concern is its getting hotter and I don't want to scarify when the soil/weather is too hot/dry)?

many thanks