Single-carrier (SC) waveforms offer significant ad- vantages in high-frequency communications due to their lower peak-to-average power ratios, mitigating channel and system impairments. While extensive research has addressed dual- wideband fading challenges for OFDM systems in mmWave/THz, the investigation of these effects in SC MIMO transmissions remains limited. This paper focuses on the time-domain estima- tion of MIMO channel matrices for point-to-point systems under dual-wideband fading, encompassing both beam squint and inter- symbol interference (ISI). We propose a unified framework that accounts for beam squint at both the transmitter and receiver, as well as ISI caused by propagation delays, addressing limitations prevalent in single-antenna studies. A novel mixed- integer biconvex model provides a flexible channel estimation framework. It handles diverse delay patterns using a binary vector and decomposes the channel into path-specific matrices for smart environment integration, such as sensing and reflecting surfaces. This semi-parametric approach, estimating delays and separating path gains/angles, offers advantages over conventional methods and enables advanced optimization.