Thermal shock and heating questions

Hi guys!
Well, I started the newbie routine yesterday. My plan is to follow it rigorously for 3~4 months and hope to get any results! ( please )
I start with 5 min with only my penis wrapped in a very small towel under a hot shower. Then I stretch for 30 seconds in the 4 directions ( Should Increase these numbers though ) and after ~120 jelqs. In the end, more 5min of the hot water thing.
But I’m quite concerned about heating. I know is very important to avoid injuries and to recover, but I’m not sure if the time is enough for the heat to “reach” the inner parts.
Are There some methods to know if the heat is being enough?
And the last question and title of the topic: My shower for some reason randomly gets really cold for some secs, and I’m afraid that this abrupt change of temperature may have negative effects. Should I remove my penis from contact with the cold water or I’m just being paranoiac?

Please apologize me for any grammatical error

Avoid cold water.

Look for Kyrpa’s thread on ultra sound heat.

A heated gel bag gets really hot, much more than the shower.

Get a pitcher, fill with hot water duck your penis in. That should work too