Hi
Workflow is really good at working with any records within CRM but it does not have a clean scheduler or job runner. We can still create a scheduled workflow but we will have to achieve this using a waiting workflow which you seem don't want to go for it. Waiting workflows have their own issues and i can see why you are hesitant to go for waiting ones.
You could consider one of the following options
Option 1: Taking advantage of the best of both worlds - Workflow and Flow
What about if you create a workflow that does all you want for that particular record and then use a scheduled flow to run the workflow on these records.
Please follow the link below to know how you can create a scheduled flow
[View:https://docs.microsoft.com/en-us/flow/run-scheduled-tasks:750:50]
And follow the link below to see how you can run a workflow from Flow
[View:https://community.dynamics.com/crm/b/alexanderdevelopment/archive/2016/12/10/executing-dynamics-365-workflows-from-microsoft-flow:750:50]
In your case, you could achieve what you want using the following steps
01. Create the Workflow in CRM as an On-Demand workflow (This does not have to trigger on record events but you can set to trigger if you want to cater for scenarios like when date changes or something along the line)
02. Create a flow to trigger on a daily basis, or whatever the interval suitable for you
03. In Flow, use the Dynamics 365 Connector - List action to get all the records you want to check if the start date is tomorrow. And for the record that has start date tomorrow, run the workflow in CRM and have all your logic in the workflow - creating task or sending an email and all that stuff.
Option 2: Use only flow
You can achieve the whole thing just using flow, please see the steps below
01. Create the flow to trigger Daily or Weekly or whatever the interval suits you
02. In the flow, use the List action of Dynamics 365 or CDS connector to retrieve all the records that you want to send a reminder for
03. Loop through each record and check if the Start date is tomorrow - Using Apply Each
04. Send an email or Create Task as a reminder
05. Update the flag field or other fields on the record to mark that the reminder has been sent.
Hope this helps