The half life of test testosterone cypionate or enanthate is about 6-8 days depending on
a couple factors. Serum T will reach it's PEAK in about 48 hours after injection and then slowly drop. So for best EVEN blood levels of T, ESPECIALLY on the lowest recommended dose of 100mg/week, it is best to inject the weekly dose in two separate injections per week.
If you are doing 150 per week then you don't need to divide the dose over two weekly injections since the total dose is higher....you don't ever see a drop in serum T below 1200ng/dl(above high normal) at any time of the week with this dose.