If you have sent the sms to an Indian number:
As per TRAI regulations, you are only permitted to deliver promotional or commercial messages during normal office hours. Please refer to the following page for the full regulations
http://www.nccptrai.gov.in/nccpregistry/regulation1diccndiv.pdf.
Please refrain from sending messages after 9pm India local time.
I have contacted the customer care and came to know this information.