There are several reasons for such a rule, including prevention of market start time creep and prevention of a sales advantage to early arriving sellers. So, use the pre-market period to see what everyone one has. Most sellers do not put on display the most perishable items, such as blackberries, until just before selling begins. Of course, crops need moisture while they are growing, but near harvest time rain can be devastating. Wet conditions promote rot, plant diseases, fruit cracking and reduce time available for harvest.
Some sellers do sell by weight, but most sell by volume.
Strawberries are a marginal crop here, but the season is April. Check our seasonality list for the seasons of other crops.