When will an investment order be placed with the Mutual Funds provider after the payment is complete?

The investment order will be placed immediately after your bank confirms that your auto payment is successful. Your bank may take upto 24 hours from the time the amount is deducted from your bank account to confirm the payment. 

You can check the payment confirmation & other unit allocation details in the My Orders section on your PhonePe app after 24 hours. 

Related question(s):

Holiday Calendar for Unit Allocation and Redemption Timelines.