How long should I wait when he says "text me anytime"?

I dont want to seem too eager but I also dont want him to forget about me
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Me and this guy met in the spring and texted and flirted for a while then stopped talking he asked me for my number and I gave it to him, I accidentally texted him yesterday and we had a conversation and he said that he missed talking to me
How long should I wait when he says "text me anytime"?
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