It just doesn't work for us unless it's done pretty much as soon as we get in. Mine get the bus home so it's 4pm by the time they are in so quick snack and straight to it. DD is in kindy (reception) and has 1/2 reading books which we're expected to read every night Mon-Thur, she gets 6 sight words to learn and a memory verse to remember. Occasionally there's an optional task (eg. find as many sh words as you can in your books) which we rarely do.
DS2 is Y4 and is expected to complete his 4/5 tasks in 40 minutes (spellings, times tables, mathletics, reading etc.) He often asks for a rest before starting but I find if I give him longer than 20 minutes or so he moans about doing the work so it's kinder in the long run to make him get it out of the way asap. DS1 is old enough to manage himself.
I'm in awe of those who manage anything before school - mine leave the house at 7.50am though, I'm guessing you're later?