With most subjects it is advised to do 1 hour blocks say twice a week or something like that, but definitely don't do that with languages! The key is to do some every day. I do a half hour every day on both languages because I struggle with Irish especially! If you can't manage a half hour do at least 10 minutes, you can't cram a language! I find writing stuff out over and over helps, then saying it out loud over and over helps. Listening to music, watching programmes, reading in the languages really helps aswell. I've brought my grades up to H1s by doing this since the start of fifth year until now in 6th year. Good luck!!
This blog will give you study tips for improving your languages:
This guide is for general advice on Irish:
This guide is for general advice on French:
Hope they help :)