Please refer below image for project cycle estimation details:

System Conversion in short is typically the fastest option, an approach that converts any SAP ECC 6. x system running on any database to SAP S/4HANA, preserving your existing configuration, customizations, and historical data. This approach allows a rapid technical conversion, adding innovations gradually for users.

The major teams involved in a conversion project are the

Technology Team (responsible for executing the Software Update Manager (SUM) tool in all the platforms (Sandbox, Development, Quality, Pre-Production and Production));

Functional Team (responsible for pre-check for Software Update Manager compatibility, Functional factory, Migration to new Finance Tables, Credit Management and Material Ledger activation, involving different Lines of Business);

Security Team (adjustment of roles for new Fiori applications);

Advanced Business Application Programming (ABAP) Team (responsible for the custom code adaption, SAP S/4HANA code remediation etc.)

Fiori Team (responsible for setting up the Fiori Launchpad and Launchpad designer).

To begin with a conversion project, we first need to discuss and decide on the data cleansing. This includes master data as well as transactional data cleansing (Cleansing historical data) based upon the customers’ statutory requirements. The data cleansing helps in reducing the database size to be converted proving beneficial to the technology team for a smooth conversion.
 

(Image Source: SAP)
 

Starting with the Prepare phase, the base document to start with the conversion is the Readiness Check Report.

Readiness Check is a high-level analysis to get a Results Dashboard and download to a Results Document with details of Active Business Functions, Add-On Compatibility, Custom Code Analysis, Recommended Fiori Apps, SAP S/4HANA Sizing, Simplification Items, Business Process Analytics and Data Volume Management.

The main elements that need to be analysed from a functional point of view are – Active Business Functions, Add-On Compatibility and Simplification Items.

Active Business Functions – The active business functions, enable us to use specific new features and enhancements for our various business processes.

Add-On Compatibility – The check analyses how many add-ons are installed in the system, with the help of a Maintenance Planner whether they are compatible with SAP HANA.

The Maintenance Planner is a solution hosted by SAP that helps you plan and maintain systems in your landscape. The Maintenance Planner also helps the customer get a view on the compatibility status of the Add-Ons on his/her SAP ECC system before system conversion/upgrade to SAP S/4HANA.

Simplification Items – By executing the above-mentioned report you can get a list of Simplification Items that are relevant to the specific customer database and must be investigated before converting the SAP ECC system to SAP S/4HANA.