That's not something you do via /stimulustimes or -frames. How stimuli are selected from a given pool is solely to be controlled via the respective *stimulus* element, here the <text> element.</values>
/ 1 = " PTTVPS "
/ 2 = " UUOIOOP "
/ items = pleasant
/ select = values.myvalue
/ ontrialbeging = [values.myvalue=1]
/ stimulustimes = [0 = word]
/ timeout = 4000</trial>
However, I fail to see the merits of this approach. If you want a <text> element to just have a single item, why would you want to specify more (here two)?