What hotel is he staying in? Realistically, there isn't alot of sightseeing and things to do in the evening.
Someone suggested the Tech Museum, which is cool. Here's a link:
http://www.thetech.org/ However, most weekdays it's only open until 5 (6 on Thursdays and 8 on Fridays.
Here's the link to the WInchester Mystery House:
http://www.winchestermysteryhouse.com/index.cfm
But, the last estate tour is at 3 and the last mansion tour is at 5.
I personally think the Rosicrucian Museum is cool:
http://www.egyptianmuseum.org/ But, once again, only open until 5pm.
Depending on where he is staying, Santana Row is nice, too.
http://www.santanarow.com/
There are lots of nice restaurants. A budget meal can be had at Plutos. I ove the Village Bistro (pricier). Roux Louisiana Kitchen has a nice happy hour. I aso like AMber India and Yankee Pier.
There are wineries in close proximity to Santa Clara, if he has an afternoon off or stays the weekend.
Savannah-Chanelle Vineyards and Cooper-Garrod Vineyards in Saratoga
Byington Winery in Los Gatos
Los Gatos has a nice downtown area, also.
Does he like sports? Santa Clara University has a baseball game on APril 6 at 6pm.
I live right on the border of Santa Clara and work there, so am pretty familiar with the area.
I hope he has a nice trip.
Julia