Have you looked at the Tufts University test that shows the recurrence rate in the same breast with and without radiation and hormone therapy? https://www.tuftsmedicalcenter.org/ibtr/ Hypo-fractionated radiation is often recommended for patients with early stage breast cancer. It is just 16 sessions without boost. As for timeline, it is my understanding that radiation should start no later than 12 weeks from surgery, while 6 weeks is optimal.
The oncotype dx test results will let you know your distant recurrence risk with hormone therapy. Radiation is a local therapy that lessens local recurrence and potential future surgery that might entail mastectomy. It is considered optional for women over 70 yrs old with early stage cancer and no nodal involvement because it does not affect mortality rates given the low aggressiveness of cancer at older age and the possible co-morbidities of older patients.

Radiation should ideally start at 6 weeks but I did find this study on breastcancer.org that says under 8 weeks.
https://www.breastcancer.org/research-news/delaying-rads-after-dcis-incr-recur-risk
Would you be comfortable asking you doctor what the considerations are for only offering full breast radiation, ie; cancer grade, type of cancer, risk of recurrence with or without radiation? If partial breast or targeted radiation is available to you, or available in your area?