start the wallet rpc like this without setting a daemon
./monero-wallet-rpc --rpc-bind-port 18082 --wallet-dir . --disable-rpc-login --log-level 4 --non-interactive

so it will  respond instantly to requests.
afterwards you can set the daemon connection like so:
#!/bin/sh
IP=127.0.0.1
PORT=18082
METHOD="set_daemon"
PARAMS="{\"address\":\"node.sethforprivacy.com:18089\"}"
curl \
    -u username:password --digest \
    http://$IP:$PORT/json_rpc \
    -d '{"jsonrpc":"2.0","id":"0","method":"'$METHOD'","params":'"$PARAMS"'}' \
    -H 'Content-Type: application/json'