How to do metta for a long time (before sleep)?

Usually i do a short metta after vipassana - saying good wishes to myself than to someone close than to people i like lsess and less and in the end include all beings i want to do metta before sleep so i can sleep better- but it usually takes me a long time to fall asleep no matter the stuff i tryed --- so in case i have an hour maybe two before sleeping - or even 10 minutes is a long time for me to do metta how do i extend the metta time ? - just repat the metta cycle again and again and again ?