How many hours per credit over summer? Is this too much?

I try and take under 15 credits per semester to keep things balanced, and with the intent of taking summer credits.

This summer, I am currently looking at one online class that is three credits over eight weeks and one in-person class at four credits. The in-person class has a two hour lecture and a 1 hour discussion, and meets 5 days a week for those four weeks.

There’s going to be four weeks of overlap between these classes at the beginning. Is this going to be too much work? Is it worth investigating with the professor(s) to see how much work they anticipate daily/weekly?

Are they both 8 week classes?

8 week classes go twice as fast as a normal semester (15-16 weeks). So you would expect twice as much time in class and doing homework. Assuming these are both 8 week classes, If these overlapped it would be like taking 4.5 3 credit courses at once which is doable. This is assuming you are not doing much else.