Riolu's friendship must be at least 220 as it's max happiness base stat is 225 and you must level riolu up during the day. The possible ways to do this are:
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If you want riolu to evolve, make him happy
It evolves when it is happy during the daytime.
Riolu evolves from happiness. If he's really happy he will evolve. Normally around levels 26-34.
answer riolu doesnt evolve by level it evolves by care and love
Riolu evolves when you have maxed out its friendship, it will evolve at the next levelup during daytime.