For your email marketing needs, several platforms offer robust automation features that allow you to schedule emails based on specific dates without the hassle of manual input. Mailchimp is a popular choice that enables you to set up automated campaigns triggered by dates in your audience data. You can easily import your spreadsheet and use the dates to initiate emails, plus it provides professional-looking templates to enhance your messages. Another strong option is ActiveCampaign, which allows for date-based automations and offers customizable fields for easy importing. It also provides a variety of professional email designs. Sendinblue supports advanced scheduling and CSV imports, enabling you to automate emails based on the date fields from your list while also offering responsive templates. ConvertKit is another viable choice, providing tagging and automation features based on dates, along with clean, minimalist email designs. Lastly, GetResponse allows for date-based automation and easy spreadsheet imports, along with various customizable templates. For your specific needs, ActiveCampaign or Sendinblue might be the best options, as they offer advanced date-based automation with user-friendly interfaces and professional templates. To get started, export your spreadsheet into a compatible format like CSV, sign up for a trial of the selected platform, import your contacts and date information, and set up your automation to send emails 24 hours before the specified times. This will help you achieve timely and professional communication with your audience.

I have been using Constant Contact. They have plans where you can schedule emails by day and time. The company is extremely credible and they have lots of events you can attend to learn about email marketing. You can create templates or use your own. You can even import PDF's.They even have a plan for resending emails to non-openers

You can use Brevo or other SMTP email service provider

I completely understand where you're coming from. I also want my email communications to be efficient and professional, especially when dealing with specific dates and times. For my needs, I found that using an email marketing platform like Mailchimp or ActiveCampaign could be really beneficial. They allow for automation and can handle custom data imports from spreadsheets quite well.

With Mailchimp, for example, you can import your list directly without needing to select each date and time manually from dropdowns. Instead, you can set up an automation to trigger the emails exactly 24 hours before the specified events in your spreadsheet. ActiveCampaign offers similar functionality with a focus on automation and better customization for email design, which might help in achieving that professional look you're aiming for.

I recommend checking if these platforms allow you to format your email templates according to your branding needs, as this could definitely elevate the professionalism of your communications. It might take some initial setup, but in the long run, it'll save us both a lot of time and effort!