Implementation of the Base Station Processing Chain of NB-IoT Random Access Channel(narrow-band prach) on Digital Hardware

while plotting the Narrw-band PRACH signal using the default code whic is given to generate the time domain signal in the LTE toolbox, in the workspace it shows the grid value as follows,

the 48 is num of subcarriers in the frequency domain. but why in the time domain it shows 286 slots? what is the reason for the value? can anyone explain deeply ?