Stacking checks into the same day isnt very realistic, its true : moving to a four week scheduling tool would probably be a major effort as well : but some sort of compromise could be done with the current one-week view.
I'd imagine it could go something like this : your staff level determines how many checks your team can run per day, for your fleet types. So, as you schedule your planes, when a particular day reaches its limit, you could be asked if you wish to re-schedule to a 'free' slot or pay a penalty to keep it on that day : call it 'overtime' or 'temporary additional staff cost'. Some of us like to avoid checks on the 'busy' days like Monday/Friday and might consider the penalty acceptable to keep those days open to fly and earn.
I dont see that being too difficult for newer players, as you can see pretty easily from the overall scheduling view where a/b-checks are falling over the week. If a player wanted to micro-manage maint scheduling down to the finest level, much as some do pricing, then they can. Such a system should be flexible enough to accommodate both.
Maybe this would also open up the possibility of boosting your maintenance staff from the 'personnel' page : say to 120%, which would then allow you to stack more checks into a day and thus avoid the penalty : the penalty cost would need to be worth avoiding to make that idea attractive though.