Realtime flows are processing messages at sub-seconds speeds which are guaranteed by the always-up condition of Docker containers. When all the containers are up and running it can process messages in less than 500ms and this is in the worse case. The nature of Realtime flows is unique and the caveats are unique as well.
Please Note: We can only guarantee sub-second speeds between Docker containers within the integration flow.
If your component, which resides in any specific container, polls data from outside source the speed of that polling is completely dependant on the service provider of that source. For example, if it polls the data from Salesforce it will depend on how fast Salesforce would answer.
When you first start the flow it will take longer to process the very first message. We call this period a warm-up time. It will usually take a minute or so to rise all the containers and make them operational. All the consecutive messages will just fly through like a lightening.
The warm-up time would also need to be considered when you re-deploy your component code and re-launch it again.