You can use the split node in conjunction with the delay node set to rate limit and a time greater than process time, once process complete just send flush = 1 to delay node to release the next.
e.g.
[{"id":"7eb5e487ab7668c6","type":"inject","z":"366a43adb328cf95","name":"","props":[{"p":"payload"},{"p":"topic","vt":"str"}],"repeat":"","crontab":"","once":false,"onceDelay":0.1,"topic":"","payload":"[1,2,3,4,5]","payloadType":"json","x":160,"y":60,"wires":[["128da9ebf14e652a"]]},{"id":"128da9ebf14e652a","type":"split","z":"366a43adb328cf95","name":"","splt":"\\n","spltType":"str","arraySplt":1,"arraySpltType":"len","stream":false,"addname":"","x":310,"y":80,"wires":[["2516c585c614ca26"]]},{"id":"2516c585c614ca26","type":"delay","z":"366a43adb328cf95","name":"","pauseType":"rate","timeout":"5","timeoutUnits":"seconds","rate":"1","nbRateUnits":"60","rateUnits":"second","randomFirst":"1","randomLast":"5","randomUnits":"seconds","drop":false,"allowrate":false,"outputs":1,"x":480,"y":80,"wires":[["2e32b43911ef6645"]]},{"id":"0ded4ecceb959c0f","type":"inject","z":"366a43adb328cf95","name":"reset","props":[{"p":"reset","v":"true","vt":"bool"},{"p":"topic","vt":"str"}],"repeat":"","crontab":"","once":false,"onceDelay":0.1,"topic":"","x":130,"y":120,"wires":[["2516c585c614ca26","2e32b43911ef6645"]]},{"id":"37b1174d8b84ce12","type":"function","z":"366a43adb328cf95","name":"procees and send flush","func":"msg.payload = msg.payload*10\n\nreturn [msg, {flush:1}];","outputs":2,"noerr":0,"initialize":"","finalize":"","libs":[],"x":670,"y":20,"wires":[["7c729254e37390c0"],["2516c585c614ca26"]]},{"id":"2e32b43911ef6645","type":"delay","z":"366a43adb328cf95","name":"simulate proccess delay","pauseType":"delay","timeout":"5","timeoutUnits":"seconds","rate":"1","nbRateUnits":"1","rateUnits":"second","randomFirst":"1","randomLast":"5","randomUnits":"seconds","drop":false,"allowrate":false,"outputs":1,"x":430,"y":20,"wires":[["37b1174d8b84ce12"]]},{"id":"7c729254e37390c0","type":"debug","z":"366a43adb328cf95","name":"debug 101","active":true,"tosidebar":true,"console":false,"tostatus":false,"complete":"false","statusVal":"","statusType":"auto","x":810,"y":80,"wires":[]}]