Is there a way to change to default due date on invoices from 30 days to same day?

Yes, you can change the default due date by editing the default payment term, @apt1.

First, create a new term from the Terms drop-down on your invoices page.

Here's how:

1. Go to your Sales tab and click on the New invoice button.
2. Click the Terms drop-down and click +Add New. 
3. On the New term window, set 0 as the number of days for Due in fixed number of days. 
4. Click the Save button once you're done. 

Once you're done, go to your Account and Settings to set it as the default term.

Let me walk you through the steps:

1. Click the Gear icon and choose the Account and Settings.
2. Go to the Sales tab and click the Pencil icon in the Sales form content row.
3. Click the Preferred invoice terms drop-down, then choose a term.
4. Click Save, then Done. 

After setting it as default, it will be automatically applied to your invoices moving forward. See the following article on how to Adjust Invoice Payment Terms in QuickBooks Online. Also, here's more information on how to record invoice payments in QuickBooks Online.

I’m always here if you need further help with your invoices. Let me know in the reply section below. Have a great rest of the day!