Is visiting the doctor during the daytime in Ramadan for hair loss considered unlawful?

The basic principle is that it is not permissible for a woman to seek medical treatment from a foreign man unless there is no female doctor available, or no male mahram [unmarriageable kin]. This must be done while observing the Sharia regulations. There is no blame upon her in doing so in cases of need or necessity. Nor does it matter if this occurs during Ramadan, as there is no sin involved.