"Congratulations on getting a good deal! You shop like I do--looking for those end-of-season plant bargains! You got good advice at home depot. When you can tell that the grass and other deciduous shrubs in your area are greening up, go ahead and snip out the dead parts on your shrubs. I also recommend adding some fresh compost around the base of the shrubs. This will act as a mulch and as a slow-release fertilizer. You want to feed the shrubs to encourage new growth. Please make sure the shrubs get about an inch of water per week this growing season--through rainfall or the hose/sprinkler. You want to baby them this year so that new growth is encouraged and then sustained. But STOP WATERING about August. You have to stop then so the shrubs harden off for winter. Mulch your shrubs good in fall AFTER the ground freezes (not before). If your shrubs will be exposed to high winds in winter, you'll need to spray them with Wilt-Pruf or another anti-desicant product in fall. A garden center should be able to help you with this. Arborvitae are North American natives, so your plants should recover and do fine.
Please note, though that they are susceptible to winter drying (that's why you have to harden them off/prepare them for winter by stopping watering in August), so you need to protect them in winter if they're exposed to wind.
Also, they have shallow root systems. Keep an organic mulch around the base of the shrub. When it decomposes, replace it. Don't bury the existing root system, though, under like 6 inches. That will smother it.
This is a great link all about arborvitae--this guy is a really an expert:
He's in North Dakota, but I've read his stuff. It's great. Happy gardening!"