When implementing Triple Speed Ethernet with 1588 IP Core, why are the timestamp options disabled?

Description

To enable the Triple Speed Ethernet IP core timestamp options:
- Select Core variation: 10/100/1000 Mb Ethernet MAC with 1000BASE-X/SGMII PCS
- Turn off 'Use Internal FIFO'
- Select Transceiver Type: GXB
- Turn on 'Enable SGMII bridge'