Salinity and live rock :S

[gottafindnemo]

So, i have to pick my live rock up at the airport in 2 hours, im 99 percent sure my salinity is outta wack but my hydrometer is garbage amd my refrac doesnt get here till wednesday. I had it at 1.024 a few days ago, but have noticed quite a bit of evap and itd only a 25 gallon tank. Ive asked other ppl amd they say salinity isnt a big issue for adding live rock, was wondering your opinions? I dont reeally wanna add more water to the tank until after the live rock is in, incase of overflow haha