What time do you finish work?
No, I'm not hitting on you, just trying to prove a point. Your end of day might be 5pm, 6pm, 9pm or if you work shifts even 4am!
My point? Vague responses can lead to misunderstandings and disappointed customers.
Instead of saying ASAP (as soon as possible) or EOD (end of day), pick a time and offer an option.
Rather than "I'll call you back ASAP", say instead "Let me look into this and find out for you. It should take 20 minutes. Do you prefer a call or an email?".
Tip: Build in some margin time. Although the task should only take 10 minutes, chances are you will be interrupted, so be realistic.