Only take caber if you have prolactin side effects from the tren. If you’re not sure, get blood labs to know. Too low or too high are equally bad. If tren ups it, you want to lower it just enough. If you are only using test you don’t need caber at all.
You can take it the day you pin if you want - doesn’t really matter as long as you are consistent with timing and days (if you are taking 0.5 twice per week then always to Monday and Thursday and don’t miss).