I suggest that you replaced your timestamp within the origin qvd with a date and a time like:
date(floor(timestamp)) as date,
time(frac(timestamp)) as time
to reduce the number of distinct fieldvalues - for the background, see: The Importance Of Being Distinct and it will reduce the size of the qvd quite significantly and all following loadings should be a lot faster. Also it makes it easier to create such exists() temp-table like suggest from mkelemen and I'm not sure that the date-approach there will be really work with your timestamps.