Vowel length slip-ups that native speakers actually care about?

Hey guys. I've been focusing on pronunciation lately, especially double consonants and long vowels. Beginners always get told they'll say "grandma" instead of "aunt" if they mess up, but does it actually cause real confusion in casual speech? Like if I cut a long 'o' short in a fast sentence do people still get it from context or does it totally derail the conversation? Just trying to see how much I need to obsess ov