In Jainism, images or idols of Tirthankaras are used as aids to meditation and inspiration for the devotee. There isn’t a single, fixed "start date" for idol worship in Jainism, because:

• The reverence for Tirthankaras and the use of symbolic images appears from very early in the tradition, but the form and emphasis of idol worship vary between traditions.
• Śvetāmbara and Digambara communities developed their own practices and iconography over time. Śvetāmbara temples in particular have long featured large, richly carved images, while Digambaras historically placed greater emphasis on renunciation, though images are also used in many Digambara practices today.
• In general, images serve as focal points for remembrance of a Tirthankara’s teachings and for veneration (puja), rather than as objects of worship in the sense of creator-deity worship.

If you want, I can give a concise summary of how idol practice differs between the Śvetāmbara and Digambara traditions, with specific terms and examples from Jain scriptures.