I think powder stand a little bit longer as long as the color remains white.

attached information from sigma-aldrich (Cat No. B8049)

To prepare a concentrated stock solution, 1 tablet will

dissolve in 100 ml of N,N-dimethylformamide (DMF,

Catalog Number D4551) with a final volume of ~125 ml

(80 mg/ml final concentration), or 1 tablet will dissolve

in 180 ml of dimethyl sulfoxide (DMSO) with a final

volume of 200 ml (50 mg/ml final concentration). These

stock solutions can be frozen at –20 or –70 °C.

Storage/Stability

Store the tablets at –20 °C. When stored at –20 °C, the

tablets are stable for at least one year. Tablets are

good as long as color remains white.

Thanks alot.