Please Help with Excel and PI

I have a simple question :

={PIArcVal("F:SUB:SPQ:xxx/25/xxxx:33258004001::M:S:M:xxxxx:::A";"27-dic-13 04:17:27";1;"SERVER";"previous")}

What I need is to have he daeime on a CELL, and refeence it .... How can be done ???

I have several ows with tags and I need to be able to change the date and time of value recovery.

Thanks in advance, Merry Chrismas and have a happy new year !!!