There is almost no situation where it makes more sense to bill hourly instead of daily, unless you're really junior. And frankly, if they want you at all, they should be willing to go in for a week.
I'm totally at odds here with this statement, repeated by others here in other words.
Look - in some industries, working 10 or 11 hours is one 'day.' As an hourly consultant I'm hedged against this, which is super common in financial environments. Maybe the experience you guys have is in less stressful, less demanding worlds.
Agree. There's probably a reason why lawyers and accountants bill by the hour. FWIW I get the impression that the folks here holding their nose at the idea of billing by the hour, actually are billing by the hour, just in 40h quanta.
The problem with forums such as this is, while most of us are in a tech or related field, we're from all over the world, at all income levels, in all sorts of industries. I can tell you that NYC and London hourly contractors are more hedged against a terrible existence of 10+ hours a day, on average, than daily rate contractors. So much so that it's actively harder to find hourly than daily rates. Employers (or clients if we should call them this) aren't stupid, they're interested in maximizing cost/benefit.
Let me add something else. It depends on seniority and connections. If you folks are very senior-level software or systems architects, known in the business world or Twitter or through established experience, you can 'set the tone' and of course it makes more sense to, as mentioned above, charge weekly versus daily versus hourly and so forth.
In my industry (DevOps and Systems Infrastructure) it's incredibly elite to reach that level. I'd have to be blogging and doing presentations at tech conferences to be able to go to a Fortune 500 company and dictate project-level Scopes of Work. And perhaps one day I'll get to that! But my point is that this is an elite percentage of consultants.
Look - in some industries, working 10 or 11 hours is one 'day.' As an hourly consultant I'm hedged against this, which is super common in financial environments. Maybe the experience you guys have is in less stressful, less demanding worlds.
Hourly is a hedge against exploitative clients.