A temporary endocrine gland in the human body is

The corpus luteum is the temporary endocrine structure formed in the ovary after ovulation. It is responsible for the release of hormones like progesterone, estrogen, etc.
The pineal gland is a small endocrine gland in the brain of animals. The pineal gland produces melatonin that modulates sleep patterns in both circadian and seasonal cycles.

Corpus cardiacum: In insects, it is located posterior to the brain and function in the storage and secretion of a brain hormone.

The corpus allatum (plural: corpora allata) is an endocrine gland that generates juvenile hormones.