Hi,
> Would you happen to know how long parallel LCD's take to execute?

No, not really since it depends on how fast the actual LCD module can handle the data and commands - or rather how fast you've told PBP that it can handle it. That's what the DEFINE LCD_COMMANDUS and LCD_DATAUS does. Then of course the actual processing takes a bit too - best thing you can do is to measure it.

Perhaps you can split your data output up in two or more section and call USBSERVICE in between?
Code:
SEROUT2 PortB.0, 84, ["This is "]    '8 bytes, atleast 8.3ms@9600
USBSERVICE
SEROUT2 PortB.0, 84, [" one part"]   '9 bytes, atleast 9.4ms@9600
USBSERVICE
Of course, using the USART would be best but I guess that's not possible for whatever reason.

/Henrik.