Researchers found that abstaining from ejaculation for six days had no impact on serum testosterone levels. On the seventh day, serum testosterone levels peaked to 145.7% of baseline, and then declined rapidly on the eighth day.
-Jiang M. Periodic changes in serum testosterone levels after ejaculation in men. Sheng Li Xue Bao 2002 Dec 25;54(6):535-8
-Jiang M, Xin J, Zou Q, Shen JW. A research on the relationship between ejaculation and serum testosterone level in men. J Zhejiang Univ Sci. 2003 Mar-Apr;4(2):236-40.