Lignosulfonate-based admixtures (LS) obtained from sulfite pulping processes were the first dispersants added as a water-reducer to concrete. Less effective than the latest superplasticizers, the low cost and low environmental footprint of LS continue to allow these materials to compete in the building and construction market. In addition to the dispersion effect, LS is known to retard cement hydration. The aim of this paper is to characterize the effect of LS on the hydration and rheology of cement paste. The effect of the time at which the LS is added, either by immediate addition or after ten minutes of hydration, has been investigated. It appears that the immediate addition of LS is less effective than the delayed addition when it comes to dispersion of cement, likely due to the initial ettringite formation.