There is never an acceptable excuse for not providing your prospects and customers with support.
That's why we recommend our clients set up a helpdesk for their businesses and make sure someone checks it three times a day.
I cannot tell you how many times I have worked with a client, whose customers and prospects are complaining about the lack of support and proper follow-up, where the excuse the business owner offered was something along the lines of:
• "Oh, we don't have anyone monitor our support emails on the weekends/holidays..."
• "We try to get back to people within a 48-72 hour window..."
• "Oh, Judith runs our support email and she was on holiday for the past week..." or
• "We strictly rely on our forum or Facebook group to provide support, because it keeps our expenses low."
Each of those excuses is BULLSHIT. And none of them are professional.
We can teach you a better approach.