C. F. Keil and Franz Delitzsch on Proverbs 31:18

Pro 31:18 18 ט She perceiveth that her gain is good;         And her light goeth not out at night.

The perf. and fut. are related to each other as antecedent and consequent, so that 18a can also be rendered as an hypothetical antecedent. She comes to find (taste) how profitable her industry is by the experience resulting from the sale of its product: the corn, the grapes, and the wine are found to be good, and thus her gain (cf. Pro 3:14) is better, this opened new source of nourishment productive.

This spurs on her active industry to redoubled effort, and at times, when she is not fully occupied by the oversight of her fields and vineyard, she has another employment over which her light goes not out till far in the night. בּלּילה is, as at Lam 2:19, a needless Kerı̂ for the poetic בּלּיל (Isa 16:3). What other business it is to which she gives attention till in the night, is mentioned in the next verse.