The 98 model year changed mid production run from the hydraulic tensioner to the mechanical (I just did my daughter's that had the mechanical). The parts to the mechanical system are identical to my 2001 V70 and that interval is 105K miles. If you have the mechanical system, then I'd go 100K if you have the hydraulic system go as Klaus suggested and do it at 80K. I've never done a hydraulic, but the mechanical system is quite easy. I'd highly recommend counting the notches in the belt between the timing marks before taking off the old one so the new goes on the same. I'd also hand crank 720 to make sure there is no interference prior to starting, and then running the engine for a short time prior to making the final tension adjustment if it is a mechanical system. Good luck and please let us know how it goes.

Jerry
01 V70 T5a
101,000