Can booking a flight or an hotel stay be more expensive during the weekend?

This answer is not supported by any references. However, I don't think so, for several reasons.

First it isn't obvious a priori that there is a surge in bookings on the weekend.

1. Time zones exist. Right now in Beijing it's still the work day for another hour, but in Sydney the traditional weekend has already started. Meanwhile in London it's still Friday morning. In poor old Honolulu, it's still Thursday night!

2. The days of the weekend are different in different countries. In Dubai it has already been the weekend since Thursday evening.

3. Many people book their flights when they are at work and not at home, because they are travelling on their company business, because they are taking a lunch break, or because they are procrastinating, so it isn't at all obvious that most "research" happens when they are not at work. For instance I am writing this answer right now in the Beijing working day.

4. People have shift jobs, people take holidays, people go out and party at the weekend instead of searching for flights.

[A counter argument would be, first you can segment by selling country, but actually that's harder than it sounds and quite ineffective; and second, maybe few people in China buy Ryanair flights in the UK, so the time zones are not important.]

Anyone with access to the real revenue data could tell you the answer to this, unfortunately I do not.

However, there is a more subtle problem with this proposal. These days customers tend to compare many flights or hotel options, often over several days, and through automated comparison websites or indeed by hand. That gives them a good idea of the expected market price for their excursion.

I would argue that, even if bookings are "bunched" onto particular days, there is no increase in the real willingness-to-pay. Therefore, and strictly theoretically, assuming you already have optimized the price over the week, an increase in price will act to reduce sales to a degree not offset by the marginal yield.

Furthermore, if you are the only airline to increase your price above the optimum (the "optimum" being based on your estimate of the supply-demand graph on the market segment, performed over a week), then you are only suppressing demand on your own flights: your competitor is the one who benefits from increased sales.

If both of you artificially increase the price at the same time by the same amount, it begins to look like price fixing, which in many jurisdictions is illegal. (Although maybe you just hired the same revenue management consultant.)

From my own experience, I usually have a fair idea of what a flight or a hotel room is going to cost me before I search for it, just based on past experience, and I've never noticed the day of the week or the hour of the day to make any difference to my expectation.