Can I stop a WhatsApp message from being delivered? If I delete a message with a single tick, does that just get deleted from my local device ( Android) or does it no longer get delivered to the recipient?
Whatsapp marks messages that have been delivered from the sender to the Whatsapp servers with a single tick, and messages delivered from the Whatsapp servers to the recipient with two ticks. After the single tick has appeared, the message is already on the server and can't be removed/aborted. 

If your data connection is slow/unavailable, you can cancel the message by deleting it before the tick appears.