First off, don't worry about studying, enjoy your Summer for god sake. Secondly, you should have like 2-4 subjects but ONE topic / chapter in each subject each night.
2-3 hours on one week day is plenty doing 2 subjects. Try to do a bit more on a weekend if u can
pal if your smart you may as well do all the study in the last month if your smart youll still be able to get the results you want the junior certs a pisstake dont waste time studying just study better and in short bursts