Thursday is an exceptionally good day for spiritual practice. In Vedic Astrology Thursday is ruled by the planet Jupiter. Jupiter is an extremely heavy planet, with significant gravitational pull.
Jupiter is associated with the guru, which in Sanskrit is literally ‘the heavy’, the one who pulls us in, the dispeller of darkness. Brhaspati (Jupiter in Sankrit) is the guru, the teacher of the gods. Brhaspati brings a sattvic, or pure quality to the universe.
Thursdays are thus known as favorable days for yoga practice, meditation, reflection, and service. This knowledge is strictly theoretical, but common to discussion or reading about Jyotish, Vedic Astrology.
My experience, however, is that somehow my motivation for practice, and the ease of sinking into asana and meditation are better on Thursdays than on other days. Is that the case for you too?