The ATtiny85 datasheet, on page 152, seems pretty clear on this:
After this fuse has been programmed device can be programmed via high-voltage serial mode, only.
But elsewhere, on page 28, it says:
If the RSTDISBL fuse is programmed, this start-up time will be increased to 14CK + 4 ms to ensure programming mode can be entered.
Can an ATtiny be reprogrammed over ISP by entering programming mode within a short interval after powering it on? If not, why is the startup delay increased as described in the second quote?