Just do it. Ive been there 3 times in January for week + periods; never run out of things to do. Watchtower face can be a fryer but just pick your day or time of day.
I remember the 'code red' in Jan 2010 when it hit 46 in Horsham we had to evac the campground so we went to the pics at Horsham. Great theatre, shame about the A/C it was nearly 40C inside!
Cool change came through that night, next day was 21 max and it climbed 1 C a day toi 28 over the next week- perfect days.
You can get some unusual side effects though, in 2009 we were cookign dinner when this amazing wind blew 10 million (+/-) mini beetles through the pines. My kids still reminisce over the Arapiles beetle pasta.