Not a slip-up at all. Look closely at the light on the side of the house as Andy is walking down the front steps to the van: warm light with cooler blue shadows: sundown, basically. Also notice how the shadows of the roof rafters are right on the top edge of the second story windows. (The later shots of this scene are all done in the shadows, so it may feel like night, but it's not, and definitely not nearly as dark as when the van returns from Pizza Planet later on.)
After Buzz hops on the back of the car, the "monkeys" scene appears, and it's the exact same sunset lighting, with the rafter shadows on the top edge of the second-story windows. The toys were probably doing the rescue attempt just minutes after the car left the driveway.
Yup, when they leave for Pizza Planet it's twilight, as when the toys are trailing the monkeys out of the window. By the time Andy and mom arrive at the gas station, it is night. Obviously Pizza Planet is not just down the road!
To sneekypete's comment about Pizza Planet not being right down the road I don't agree. It couldn't be too far away because Sid rides home on a skate board. It does seem to get dark awfully fast.
To Jazbees: I took another look at the tape and am still convinced af what I said before. It is sundown when they leave for Pizza Planet; because there WOULD BE NO SHADOWS if the sun was right overhead as it was in the monkey scene.
to Mccall and SneeekyPete-It's not like andy and his mom just drove down to pizza planet and then came back. they went at sundown, ate their pizza or whatever (probably took about an hour) and then came back at night.
About that scene, You can see the sky when all the toys are "getting on Woody's case". It shows that it is dusk, and it gets a little darker as the movie continues. When woody is yelling "YOU ARE A TOY" at woody, you can see a little light coming from the horizon line. Although, It does get pretty dark pretty quickly.