To expand on this, Webb uses the Deep Space Network (DSN) to communicate with us. It can’t stream data back 24/7. There are generally three contacts per day each lasting a few hours, but I believe this is dependent on the scheduling of contacts with other missions that also use the DSN.
Also, the science data that is sent back is a stream of packets from all the data that was taken since the last contact. The packets are arranged for efficient transmission. One of the first steps of the science data processing is to sort the packets into exposures. Often packets for an exposure are split among multiple SSR (which stands for solid-state recorder) files. Sometimes there are duplicate packets between SSRs (data sent at the end of a contact is repeated at the beginning of the next contact). Only when the processing code determines that all expected packets are present—by using clues from other subsystems—can the next step (creating the uncalibrated FITS) begin.
Also, the science data that is sent back is a stream of packets from all the data that was taken since the last contact. The packets are arranged for efficient transmission. One of the first steps of the science data processing is to sort the packets into exposures. Often packets for an exposure are split among multiple SSR (which stands for solid-state recorder) files. Sometimes there are duplicate packets between SSRs (data sent at the end of a contact is repeated at the beginning of the next contact). Only when the processing code determines that all expected packets are present—by using clues from other subsystems—can the next step (creating the uncalibrated FITS) begin.
If anyone is interested more details, the packet stuff is based on standards from the Consultative Committee for Space Data Standards (https://public.ccsds.org/Publications/BlueBooks.aspx).