I think there should be a Nissan sticker that is like a seal the timing belt cover, if its been changed that sticker would have been broken.
When I got my skyline the car yard I bought it off did a full service, changed belts, oil, coolant, plugs, etc, and fixed all the things the RAC Inspection picked up, (as part of the sales agreement).
About 4 days after I bought it I took it in to my local (trusted) mechanic who carried out a full service, replaced all the belts, oil, sparkplugs, coolant etc. It was because I didn't trust the service that the dealer had done because someone told me that they use cheap oils, belts, plugs, etc. I found that they hadn't replaced the sparkplugs, but had fixed everything on the RAC Inspection list.
Anyways if I was you I’d take the car to a trusted workshop and get them checked out because if your belt goes its going to cost a fair bit.
-michael