I used to never say no and I worked 18 hour days. Not great. I started to say no but that does piss people off. Not so great either. Now, unless it's complete

I used to never say no and I worked 18 hour days. Not great. I started to say no but that does piss people off. Not so great either. Now, unless it's completely ridiculous request, I never say no. I say something like "Happy to help! Sounds like this might take about an hour, I can pencil in that time for this project next week Thursday afternoon, looking forward to it!" If they insist it's for tomorrow I'll include in the discussion whoever needed me today and let them know there is a higher priority request. Let them fight it out. Turns out people are quick to ask for my time ASAP, but if they learn they have to confront someone else to negotiate for it, those requests die down. Or if it truly was so urgent, no problem, we'll rearrange.