S., my kid started a gifted program in third (she is now in seventh grade). And even in second, the homework got to be more. It's normal and it is doable! This is something you and he will get the hang of, I promise!
A couple of thoughts:
Don't let yourself get in a twist over other parents saying things like "In second grade he should have 20 minutes a night and no more" or any formulas like that. They are not productive or useful. You cannot say, "Oh, you did 20 minutes, time to stop right now no matter where you are in your work for the day." I hear and read a LOT online, not just here but at other parent sites, where parents are furious about their kid having "more than the 30 minutes the teacher said it would be!" and it's just wasted energy. "Minutes per night" is a guideline that some teachers give but it's best to start right now with "You get what you get, and you don't get upset."
He does not sound over-stretched from what you describe. Many (around here, most) kids have one or several weekday extracurricular activities, and he has none, so that is not an issue, truly. Hockey only on Sat. and religious school on Sun. are fine -- don't even think of those as issues! He needs outside activities, and right now yours cluster on weekends so you are, frankly, lucky this school year.
Look at how far in advance he gets assignments and how far in advance YOU know about them. Does his school use any form of "planner" notebook, where each child has a formal planner and must write every assignment and due dates into it the day they're assigned? If not -- create one just for him (or suggest it to the teacher, but I would not wait for that, I'd also do his own). Ensure that you check in every single day about what he has due. Kids at this age still don't think very long-term, so is he sometimes getting a project that's due in two or three weeks but doesn't tell you until there's a week left to go? Time to work on his telling you the same day it's assigned, then you and he figure out what days and times he'll work on it -- over the entire two or three weeks, not in the last few days, of course. He will learn early that it's easier to work a little bit all along than to say, "It's due in two weeks - I can start the second week."
Weekly spelling test study and reading log should be so routine that they don't take long -- if they are, look at why. If the worksheets are math, that should take as long as it takes -- but any good math teacher will say that if a kid is spending forever on one problem, then he should stop, move on to the other problems, do what he can on the difficult one and bring it in to discuss. Does he fully get that perfection is not the idea in homework? If he's polishing and fussing over worksheets and projects to the point it's taking forever, he is being a perfectionist -- and homework is for learning, not for being perfect.
Schedule out things with him. Use a planner he carries to school and check it with him daily. Stay in close touch with teachers especially if they fail to coordinate things, and he ends up with multiple projects due the same week as a big test, for instance (teachers should be sure that doesn't happen but...it does).
Be sure that he is doing homework efficiently during the weekdays (he should not be cramming in this much on weekends, truly). Does he have a calm place to do it, where he is not distracted by fun stuff around him? A kid's bedroom can be a lousy place for homework; even if he doesn't ever touch his toys and stuff, they're still so very present around him. Does he have a place that his sibling(s) don't disturb him and he can't overhear them playing? Or overhear the TV? Does he have ready access to all that he needs or is he popping up and down to get a pencil, sharpen it, get the book he needs, etc.? Think through the setting where he does homework.
Afterschool timeline can look like this: Come home. Snack (essential to keep their focus up). Depending on his personality and needs, maybe 30 minutes of down time, reading, etc. -- not TV or video games; too hard to stop those. Then homework starts at a specific time. (I know some parents say to give kids a couple of hours of down time or play before homework but that really depends on your kid. If my daughter waited until 5 or 6 to start homework, she would have lost her focus and would be much harder to get going. So she starts within 30-45 minutes of getting home, or it would be a struggle.) Begin each session with review of the planner and short- and long-term assignments. Ask him: "What do you think you should work on today that is due tomorrow; what is due on other days in the week and what should you do towards those deadlines?" When he's done let him blow off steam with physical play. If he's a kid who needs to do that first, before homework, do it first, by all means. You really need to think about what will give him the maximum focus and energy -- longer down time/running around first, or after. Each kid is different.
Teach him to break up tasks. For instance, say he has to turn in a vocabulary list each week where he has looked up the words and writes sentences with them. Due every Wednesday. So Monday becomes word homework day (looks them up, writes down meanings) and Tuesday is the day to write the required sentences and check it all over.
Praise him a LOT for using time wisely: "Wow, your project is due in two and a half weeks but you already have the books checked out and are starting your notes -- that is a great use of time, just like an older student would do." And so on.
This was a tough week for him (and you) with two projects due at once but not all weeks will be this way.