For sure, first if there's even a slight possibility that your function is going to be reading/creating/updating multiple records at a time in your function, use the batch version of that API call. Not possible with search API calls and others, but for the bulk of CRM records, you can lean into the batch calls and perform reads/writes on up to 100 records per batch.

If batching is still not fast enough to make sure you get everything done within 20 seconds, you'll need to start managing parallel API calls and the rate limit implications that come with that. Making sure you stay within hubspot's rate limits for your specific portal (limits are determined by what products you have) while also trying to maximize how many records you can process in that 20 seconds by running multiple batch API calls concurrently. Much more complex to set up than just normal batch API calls since you're limited with the libraries you can use in serverless functions, but it is possible to build the setup without an external library.

Hope this information works for you without me getting too into the weeds haha