Burned PCB with reflow soldering
Temps are way too high and times are too long.

I manually reflow also using Kester EP256,
https://www.cmlsupply.com/kester-ep256-lead-solder-paste-63-37-150g-jar/

I have a multimeter with thermocouple probe, Extech EX330.
http://www.testequipmentdepot.com/extech/multimeters/compact-digital-multimeters/autoranging-digital-multimeter-600v-10a-non-contact-voltage-detector-temp-function-ex330.htm?ref=gbase&amp;gclid=EAIaIQobChMI6-uRsOq13gIVlUoNCh0r_wsqEAkYAyABEgJG1_D_BwE
Purchased at my 'local' electronics supply store for around $40.  I've gotten a lot of use out of that probe.
I place the probe to sit just above the boards, the door closing holds it in place. The toaster oven is an ancient Sears toaster oven with 4 heating elements, and a tray to place the boards on.

Start the heat: turn temp to high, back it off when it hits 145C, the oven will continue heating a little, let it settle around 150C. Let it sit there 90 seconds.

Start the heat again: turn temp to high, back it off when it hits 185C, work the heat on &amp; off, keeping it above 185C and below 205C, for 90 seconds.  205C is important, quite a few parts show 205C as their never exceed temperature.

Turn the heat off, open the door a little to let the heat start escaping slowly. When the temp drops below 180C, smoothly open the door fully.  Let the tray cool some more, then remove the tray and let it cool fully. I let mine sit on a stove burner to finish cooling, they can take high heat.