Blackfords don’t recommend mowing until the new turf has rooted. This can easily be checked by lifting up a corner of a turf to see of the roots have attached to the soil. If it is firm then it can be mowed but take care not to disturb any other part of the lawn area especially by the use of rotary mowers which create suction.
Your mower should be set to the highest setting as it is important that the lawn is not scalped during early cuttings.
Mow your law often, each time removing no more than one third of the grass height. Once fully established the grass height can be reduced gradually to your ideal level. Optimum heights are between 15mm and 35mm depending on turf quality but 25mm is normal.