The Bill and Ted movies obviously don't take history that seriously - after all, the premise is that two slackers are in danger of failing their history class when a man from the future hands them a time machine and tells them to recruit whomever they would need from the past to make a kick-ass final presentation - but oddly enough it does end up saying something poignant about the way time works.
I used to listen to a lot of classic rock radio when I was growing up, and because it's a backwards looking format it's hit to miss ratio is much better than modern radio. They have culled out the tracks that were just okay in favor of the most beloved songs, while contemporary stations still have to try to figure out what people like through trial and error, playing as many forgettable trifles as future classics. (Of course, all currently operating radio stations have probably overly culled their playlists by this point, but let's not go down that rabbithole.) The point is that the past appears in our present in a concentrated form but the present is much messier, and any time you make that juxtaposition you almost have to ask yourself how your life will or will not be passed over as time marches onwards. Bill and Ted's Excellent Adventure inadvertently makes this comparison because the characters of Bill and Ted are incredibly 80's specific, but all of the figures they collect from history have left footprints that have lasted for centuries.
Of course, the Socrates and Abraham Lincoln of this movie don't have any real resemblance to the historical Socrates and Lincoln, but it's an interesting contrast nonetheless, because we're so much closer in time to the world Bill and Ted lived in than we are to their times, but Bill and Ted's world feels so much farther away in many ways. (It helps that Lincoln's face is on money, so he seems more omnipresent than these outdated characters would.) Our titular heroes are incredibly enamored of Eddie Van Halen's guitar playing, which seems weird today, not just because Van Halen hasn't been a powerful culture presence for going on two decades now but because it's been so long since we fetishized anyone for their guitar prowess. (If I remember correctly Rolling Stone tried with John Mayer, but I think everyone (correctly) told them to fuck right off.) Once you add up all the signifiers that tie Bill and Ted to the time it was made - their surfer dude lingo, their musical tastes, their clothing (which mixes shirts that are cut off above the bellybutton with extra layers like trenchcoats or vests) - and then you juxtapose those against the historical figures that they've recruited you start to get a weird sense of how time preserves some things and loses the other. This movie is like a radio station that alternates between a mediocre and disposable modern pop song and songs that have been so ubiquitous for so long that it's impossible to even say whether or not you like them or merely just know them.
Or, to make another cross media format comparison: Bill and Ted's Excellent Adventure reminds me of old black and white pornography that people like Bettie Page made generations ago: because it's a moment stuck in time it retains the same fun properties that it always did on the surface, but if you think about it abstractly for a second, you can't help but think about the cruel realities of mortality. The sexual content of that photo becomes weird when you start to think about how that person no longer looks like that and might not even exist at all anymore. Because Bill and Ted are adventuring through time and collecting people we know are already dead, they are (implicitly) approaching questions of impermanence, both physically and psychically, and that's weird, because it's such a light hearted movie. But the light hearted movies of twenty five years ago can easily become reminders of how twenty five years have passed, and that isn't such a light concept. As Bill and Ted might say: Whoa.