In a buoyant market I would say it matters less if the house isn't clean and tidy (not immaculate because in a house with children, that's just unrealistic to sustain), but when the market is tougher it's probably better to get your house presented at its best.
That's not stripped out of all personal items, but simply clean (so it doesn't suggest poor maintenance), in good order (so no curtain poles dangling down for the sake of a missing screw, for example), no stacks of stuff (indicating you don't have enough storage space). With not a lot of time, I'd focus on things like that rather than worrying that the cushions clashed with the throws.
The garden should look relatively neat, so children's toys present are OK, but on top of knee-high grass is not OK. Get rid of any mess like broken pots and dead plants which again, suggest lack of maintenance. You don't have to buy new planted tubs, it's all about it looking presentable, it doesn't have to be perfect.
You'd spend a lot to get the exterior painted and it's not a quick job. If it's really bad, expect the price to reflect that.
It's the same as getting your kids off to school wearing their newest polo shirt on school photos day. And hoping it gets taken before lunchtime...