Hi Rashiqua,
Yes, you can initialize the FS45 in INIT_FS state with the watchdog window set to 0 (WD_WINDOW_3:0 = 0b0000). Note that this is effective only when the INIT_FS phase is closed, so it requires at least one good watchdog refresh (0x4D when using a default LFSR value of 0xB2) within the 256ms of the INIT_FS timeout. Then you can change the watchdog window duration to a non-zero value in Normal mode.
BRs, Tomas