  The relaxation time of a single-electron spin is an important parameter for
solid-state spin qubits, as it directly limits the lifetime of the encoded
information. Thanks to the low spin-orbit interaction and low hyperfine
coupling, graphene and bilayer graphene (BLG) have long been considered
promising platforms for spin qubits. Only recently, it has become possible to
control single-electrons in BLG quantum dots (QDs) and to understand their
spin-valley texture, while the relaxation dynamics have remained mostly
unexplored. Here, we report spin relaxation times ($T_1$) of single-electron
states in BLG QDs. Using pulsed-gate spectroscopy, we extract relaxation times
exceeding 200 $\mu$s at a magnetic field of 1.9 T. The $T_1$ values show a
strong dependence on the spin splitting, promising even longer $T_1$ at lower
magnetic fields, where our measurements are limited by the signal-to-noise
ratio. The relaxation times are more than two orders of magnitude larger than
those previously reported for carbon-based QDs, suggesting that graphene is a
potentially promising host material for scalable spin qubits.
