Prime comes in a red bottle and looks like
this. I don't know if the Top Fin brand of water conditioner will lock the ammonia up like Prime does. I personally don't use it but will pick some up after my water conditioner is used up.
40% seems like a lot but right now it will help your tank/water/bacteria through this time period.
Folks will hop on soon and tell you the strips are poo poo. I have learned so much on this site in a week and the most important lesson was about test strips. I used them and was lead to believe that my tank had cycled. I added fish. Problems arose. These nice folks recommended the
API test kit. It told me exactly what my water chemistry was, and I was NOT done cycling.
Regarding warming your water up, you should probably think about picking up a heater. Since you have a small tank you would think, "oh, smaller heater = smaller price." Wrong! A
good one will easily run you $30. Your platys will probably enjoy a temperature in the range of 65 to 78 degrees Fahrenheit. I keep my tank with platys at about 78 degrees Fahrenheit. If your fin babies get sick it will help you to have a heater because you may need to adjust the water temperature to aide the fish. (Think of giving them a little fever.)
Monitoring your water chemistry often, daily if I am not mistaken, will help you see the trends. One of the Pros can help you out with the link.
This is just a start... I am born-again noob. When I was first into fish I had no clue about all of this stuff. I just did what my then-boyfriend did. (DUMB!) Anyway, this should get you started until one of the Pros posts.
Good luck!