Directional selection acting upon a beneficial recessive allele will take longer to push this allele to fixation than for a beneficial dominant allele. Assume the selection coefficient is the same for each case.

It's true ...

Explanation:

Under the light of Mendel's laws of segregation and independent assortment, the ratio of the hetrozygous alleles always remain constant no matter what the circumstances are.

In the case of a dominant allele, it is very easy to be selected even when joined with a recessive part because that's the way of nature and in hetereozygous condition only the dominant phenotype appears and recessive expression gets masks din the process. It means it requires only one dominant parent to be major in the population. However, in the case of recessive allele, it's phenotype only appears when both of the parent recessive alleles are equally participating. That's why the recessive population is very low due to less rational selection.